D-A12i 419 REDISTRIBUTION REACTIN F EMBY TRANSITION METAL..(U) MICHIGAN UNIV ANN ARBOR DEPTOF CHEMISTRY W A GUSTAYSON ET AL. 29 OCT 82 TR-4

UCASIFIED N98814-78-C-Bi I F/G 7/3 N

MEMO

ND

1111 1 118 12.811,6

MICROCOPY RESOLUTION TEST CHARTNATIONtAL @UR&AU OF StAAOS - 1963 -A

- -.... - - -I I I I I - I -l -_ - -,- - - - - -

SECURITY CLASSIFICATION OF THIS PAGE (IN,., Date Entered)

REPORT DOCUMENTATION PAGE READ INSTRUCTIO{SBEFORE COMPLETING FORM

I. REPORT NUMER 12. GOVT ACCESSION NO. 3. RECII.IENT'S CATALOG NU34SER

Tech. Report No. 4 -4. TITLE (and Subtitle) S. TyPe OF REPORT & PERIOD COVERED

Redistribution Reactions of MethylSiloxanes Catalyzed by Transition Metal Tech. Report, 1982Complexes G. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(s) S. CONTRACT OR GRANT NUMIENiSa)

W.A. Gustavson, P.S. Epstein and N00014-78-C-0191M.D. Curtis

S. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK

Department of Chemistry

'I" The University of Michigan NR 356-674o. Ann Arbor, MI 48109

It. CONTROLLING OFFIUCE NAME AND AOORESS IS. REPORT DATE

Office of Naval Research-Chemistry 10/29/82

%-C Arlington, VA 22217 25

14. MONITORING AGENCY NAME & AODRESS(IN dfferenf Itm Controlling O1ee) IS. SECURITY CLASS. (Of thi "e t)

UnclassifiedIS.. DECLASSIFICATION/OOUUGRAOING

SCNEOULE

I. DISTHIEUUION STATEMENT (of this Reprl)

Technical Report Distribution List GEN and 356B

v7. ciSTRIUUTION STATECMNT (of the abstact enteted In Stock 30, It differe bow Report ).

.NOV 1 5 1982

IS. SUP*PLMEN4TARY NOTES _ ""-

Prepared for publication in J. Organometallic Chemistry A

It. KEY WORDS (Continue 0n ,.vers* aid* II neceSAwY A ldentify by block nummbeJ

S iloxanes MetallacycleRedistribution IridiumCatalysis PlatinumTransition Metal Rhodium

C :-2. ABISTRACT (Com, me an reverse side It necesewyl end Idemfifr b), black Rmber)

Siloxanes containing at least one Si-H bond undergo a redis-

tribution reaction catalyzed by transition metal complexes of Ir,Lau Rh, and Pt. A new metalla-cyclodisiloxane of Ir is described.

___j

DD IAN73 1473 82 111i 0 6SECURITY CLASSIFICATION OF THIS PAGE (*boq Date Entered)

OFFICE OF NAVAL RESEARCH

Contract No. N00014-78-C-0191

Task No. NR 356-674

Technical Report No. 4

Redistribution Reactions of Methylsiloxanes

Catalyzed by Transition Metal Complexes

by

W.A. Gustavson, P.S. Epstein, and M.D. Curtis

Prepared for publication in the

Journal of Organometallic Chemistry

The University of MichiganDepartment of ChemistryAnn Arbor, MI 48109

October 28, 1982

Reproduction in whole or in part is permitted for any purposeof the United States Government.This document has been approved for public release and sale;

its distribution is unlimited.

cc e - o

Pr

1~.' T R 77%

REDISTRIBUTION REACTIONS OF NETHYLSILOXAtES CATALYZED BY TRA!IS!TION

.UTAL COMPLEXES.1

*

Wayne A. Gustavson, Paul S. Epstein, and M. D. Curtis, Department

of Chemistry, The University of Michigan, Ann Arbor, PT 48109.

ABSTRACT

> Redistribution reactions of a variety of hydrogen-substituted siloxanesare catalyzed by various transition metal comlexes of irdium and

rhodium. The products arise from breaking and rmkIng of Si-C, SI-H,

and Si-0 bonds. Siloxanes not possessing a Si-H bond are Inert under

the conditions studied. The most favored reaction pathway appears to

preferentially scrable the groups directly attached to the silicon bear-

* ing the hydrogen atom. A new cyclo-iridiadisiloxane, L(CO)(H)--

ir(i7 Nh fR) (L - Ph?', R a Ne&iO) is reported. This compound exists

in three isomeric forms-as a consequence of the spatial arrangements

of the R and He groups on the ring. --7 _

I,

-2-

INTROMICT ION

In an Investigation of small-ring metallacycles. Curtis and Greene1 found

that yc1j.-metalladisiloxanes, 1, were catalysts for the dlsproportlon4tlon

of tetra,-thyldisiloxane (E'E')2 Into dinthylsilane and oligameric siloxanes(E'DnE') 2 (eq. 1).

I 1c.-.'0 - ,2SIH2 + I", 2S(OSNh 2)nOS M 1

(EiE') (E'DOmE)

LON

LMN ; O Le (Ph?)2ycO)(H)Ir

b ((hf) 2 Pt

A mechanism was proposedIbIc in which the strain In the four mnsead ring

assisted the scission of an SI-O bond In 1 to give reactive, coordinated

silylene and silanone Intemediates. The crystal structure of la lent support

to the a . g t that the Si-O bond Is weakened In the mtallacycle.3

The proposed mchanism dealt specifically with the Irdium complex, la,

but could be extended to som of the other colexes with minor modifications.

Some consequences of the proposed mchanism are that: (1) only those siloxanes

possessing the 1,3-dihydrido functionality would undergo facile redistribution

since only the SI-H bond reacts readily with the low vlent mital cowpllei .

and the 1.3-orrangeent is necessary to form the four-embrtd ring. (2)

only M0/H exchange (see below) should occur, and (3) the oligomrs are

formed seqantally, i.e., 2[*[, - OE 1Eb2SI; E['* + VOE' - V02 E * +

me 2 S11H; EITE* EC2EO - V'D3 * ft2SIH2, etC.The generel features of the Ir-catalynd reaction seemed to fit all tese

requirements, at least at low conversons.,1c After longer reaction times,

various secondary products were observed. I order to further dlaracterin

the redistribution reaction and the effects of using different metals and

differMt shlames, the preset work was dertaken. Te results show that

the reaction Is much more colex than originally thoupe and that the originall)

proposed ietallacycle myhanis., if It Is operstive at all, cannot be the only

mchanKism Wer the groups on silicon are redistributed.

V, :-tz7UxAL

All manipulations Involving solutions of catalysts, reaction mwitares, etc.

were done with standard Schlenk techniques ejer a nitrogen atnpeit. Proton

and 13( 1H) IM spectra wer recorded on a eol JX-PS-100 spectrin r or on

a Varian T- . Ges chrontogram were obtained on an Antek 300, dual colum

InstrWmnt Iquipped with a temifrl conductivity detector. Recording and

Integration of the OC spectre were accomplished with a Helett Packard 3360A

integrator-plotter. The analytical colum mployed ws 14' x lf$* S.S. packed

with S1 S-30 on Chrosorb V P 01100. The carrier gas ws He at a flow rate

of 10 mI/nin. Typical S conditions are: |njector, 2W; Detector, 300";

temperature program: 2 win. at 40", then lncrvase at 4*1mn. to 22S. The

preparativt CC colum consisted of IS' a 114* S.S. packed with 20%; SC-30 on

chrovosorb A 40/60.

Ross spectre ware recorded an an AE1 1590 (pure componeots) or oa the

Finmega 4000 qudrupole speCtrmeter Interfaced to a temprature programumble

OC coluw. the uole being csatrolleO by Use INCOS data acquisition systam.4

wen operating in the Oc/IS node. the spectra %er ypically '"Oftehano, a

procefte NMr the CoMte 5 rbS'tScts out peaks %dch are Judged to be

beckoms dso the basis of their mass cwo tors. Parent Ions were located

eIthir by mess ma ch atogr (Iiss vs. time) or by cImcal Ion ultio tecumlques.

In casm w miss spectromtry fte "mld not resole twhedetity of

a Copods 0.g.. betbs the Isomers 9IO( s o 0 I, 01e Substance is

question ws Isolated y preutiwe K and alyzed b IN- a I 3ai40

spectrescep. Oc the identity of a coesd %as established, Its ns spectrum

-is stwod to the comptew library. Fute occw'mms of the coound to six-

to'ps could them be established by comaring Its miss spectrum with the library

spectrum peea tor peek.

The follrliq code will be used to the Tables to Indicate tae mimor Is *6ich

rio mi s taces were diatiftld: I - Cearisoo of K rvtttion tives

iod covter mtchag of t tho uns SPeCtr tO se of atheetIc sarples, 2 -

as In method 1 plus the Isolation of the loect by preparatiwe C end ualysis

of ItS Il- aidor '-CeFM spectat, 3 - aalysis based em comparlog SC raettitem

times aid IS frew mtatieo pattern with siilar SSUMta s SCCOdingV to

eIrical VVlas evloped I* te Coms of this wort S sid by others, 4 -

as tn metlods 1 or 3 plus sestituti m of Ph by Ph- 1s .

Starting sileafts wre purchaed frm Pitrero aid were distilled prior

to ws. Tetrimthyldisilosae was prepered by hydrolysis of Me2siNCl.

Obtained fru CSo'rlrg Corp. Waska's aind llkki'$as e1ewleurs.. L2(C0)Cllr

id L3Wl, nspectiwely, wore pr 1pred by literature oethods. 7 8 Smazene

uds 4tiled over potasww/bee1ophuame and distilled usder h~ imwwdiately priorto kse.

5ygtis1 of Itwrt..wtvadio.)tig~th~ip

L$C)(k IrSII(01 3)0i9~0Si~j). 3 VeU "s Cw~1ea, L$(CO)CtItr

(0.4g. 0.8 mis) "S 516"40d Is 10 a) of betmme. Them, 0OAS g (1.6 MCIs

of )1j**** octyeteamII (COVE) ".s ~4~ to give * cloudp.

yellow isowoo whica becim clerw r heatd to .wfw. Aftw stirriag at

reflus for' I tw.. tft Golveet wes inu~d vur co to gluve so 011

TrtUvgtOOM With bOOMiM/I06 O OMhe geu *It* iSI 14 M-P. 151W,1S 0#*14

besed so 10. Mhe 60 Of lWs of I Is tMe Sift 0g40 consits of toe browe

peks at do.$ ad 0.6 sad sherpw Put at 6.2. CEcA of tes POAS IS

O"Oftly cowpesed of .uelaftiol wmled e.

St. 10.91. 3.'. 15.71. resd. C. 91.4 N. 1.46; P. 6.1O4 14. 10.104 IV., 11.70

no. 1101SI sP Oc KWS aO v. stng bwe bebp" 100 - 10col

Pmstribstm %gignl. The comitom" ter @a*br~ no lstd 11W4S

* fuetmete s t e O tales. A tWtCOIteudsoy is decribed bete. tctrs Uty1

tosilams (1.6 010 4? "*1@) 1"n aa to 0 bsei" eetloo (2s 01)

cotamois M0 of (0126 mele) of (Pb9')(CO)CU~r ~ a 11 =.tuesms'e N~

* ~reectis noms us, *wow with a wetly. temmui. Islet, sod s oiI bqjble.'

(attached at the fto of the cuatet Sod cwmocted to it %'F ~Tr~ thre,"

a 1?joet). Owi the mtitl, a tatic 112 bl~i*i#t we-, "I'"tooI" the

* wee~tism Vessel. th f "h s imm" is a c"Itt teupevatur

bat for a iws. tia. bwi bulk oft he solv~t was Uiou

061:11)d Off A" tme "iwet fraction and Pot rW&Aw analysid by CC or

$elm5. This COWcotretlon t aleged for beter *terviotion of alof

IiOnSti %ftt thes cawS WkM 00e klotics of Of .wedstrtbucloo

veactieft we's fttmias the s'ectiom nous wa also titcd with a 4 =

Olawtr sideam tipped with eptiowe r K Si1g dorlovg0 the wr of

tow reaction. In afttiam, a "lweI mumi of isaml st&SW4r (m-b"Caf

or O.et) we ~ to 00e iWob soltlet atctayt

Tabi leI-IVI lti ow of the on ts Obsrd ato various 61l.m

cv-2.1 a -M N1 ode an touted wit% uostilsm intal

gwptgs. IN fttiom to a*e COVlmS listod, "iNMISa *tes e.g..

%(CO)P2*NY,(4)CF1. VCP 4 )f(ACM). OW LW('NP 1 ) CL.

ft vless 02plicitly stated etueWWOe). alse O eow ~- to aoulf" the #v=

tWh$4 AS 11*6 Ited 10 table L

S1at lemesch so met ee at loat amn S1.4 bea amte enr IN& th

C0010t"a Ofcvil Is 1461" 3IYI. Th~o Sj. 9, Cl, OW CK rense w~ftinp

to the w"s"iM of 00e tremtles souel ca)ets's UICS Cfse 'ydlstwlbtio"

of Owri*1*Silmt. Thm es pwt*1pls1lwM$I at lso er n to tow Ptm #

of a %*rid Ma"ma the tret, Mntl CMUMe. ThIS letter *mow tiat

Vol" eut too pe5S1ibi)it thet the 06orwi twctloss oto8 a I- 'ilt

atalysts by acidic intel -vq*J*- 'twv 44 towe toott vlartav.

As~ Table I shows. all to* m4 isitkatwio ptoIowis of VU' v~y be rationi-'ej

&s rising Irw. OACUAWS~t of groq*4 odw*enI tco i-m tv"lCOO"441itj

W lIN

Aws SiaI eoo- (s VuO witoV (oftw to a eirs) lovp"

W " it ""lf OIIPWW 0CWE0 tO M- 4 WS * ~SQ)O) C0tfft'i"

W311 *r 1sp 1V asiW1 (4)

tolIs by p tot lo i faoe foactum oot~imw tw tft Ir4iEI, catalysis

Of VC FVO~hi69IGM* 80 IS~ tUO fesell. OWtANE0 ft d WtA tfme ftt,#

Ifuvw, Wh Wslsr Products #Ppr to &rise from Sio/Ho exCk#^ep &S $boo

in 04. 3. Other almw products. e.g., the cyclic olgIers 0~ 3 d 04 0 can

be accounted for an fth basis of so iatemel WIIN evchamge ts Aow in

sq. Ii (I.e., CSI* ISIN * %b).

3b4IMN * (NsiO). (5)

butbeF SWIW anpe uw h loets a5104 em*mp of eq. 1 Can be

ecinbsullyH of tdo awInSOiIOl InmIOUL AluGOO 04e Could be

twC lip mm - m serstlw. a fser an m lvlqe ft"lacrotn w

oathe "is fwt Mi Slowm.' IP 9ta eoiel Ift forte rMie 01 pue ctspIt M n m iaei that goe mu.lleQy).s we at directly ieuolved 14 the

vith the lraalym Isa low* 9" is tbl I * SWU81I"- eaihm,.eots

fin. M Of tOe p mfta ibM. ONIy W Of the PfdtS tue. 0ha M-Utfipsdrose"" (Table 1) am e attrU eIm to SWO4 egs. Ie Sh-cotalyasd

mgctoi alo do me go"e the pue iatEstmbo~ predicted am to Im"Iss o tial elpw ftwtiin, I* .*'% y [03f. 00Ott. As tow*reI

~9 tft el9e' Vy' is so gvoreatsm ttl tham S 1e at all tion.

Diesetallacycle mchmnism Predicts the initial concentration of E'DE' to

be blokomr tftn that of E izE ince E'OE is thi initial. "Ist turuiovWr product.

Nonce, saw oer ewlsm mast be operative, even for SIO/H e*xchaege with~

tbe rhvhdm.b@We catalysts. (Note: oxyvm balance requires thee soles of

£ 'C to vm'AwW* o toy 80~ goetter est thW e mcism.)

The SJIlsus, potamtkYltS1loamne (EEO) and hexmtyltrislaxano

(1001". were subjected to vedistributiom woditons with 12(CD)ClIr as catalyst.

IEI *M nos t bw tUS ecoad byed- Necessary to frm a tour.amd-- Wetal Iacycle

aNd 9'K' UeS bo so to give tbe SIX-.6MMMd Mellacycle, 2tIc

0

LOaX~ ESIKI 5 (6)

(2)

UM~i Iteoaas' OR&V' e'strbwtiam, Sl~bV at a fie slcoeur than that

* ftr 111'. FItga I isoo ayep t cOncesratioa vS tilie for tOw wsdStributloo

of it, am'Co. Ise Coo rge t tyical for all tOW redistributio" reactions

%tamed to ewt. Iker is an Initial reoid do" In siloxaes aoncntration,

thee d - v a breek toss bye a slw, mm-~or~ rection. To* cer-order

tle Ceesatts fre to* data is ilwe 2 Am 6 * 10's mad IS it lO ilenlm

fec LI' -o goft", resesctively. *IVIuleg by t00 cnetratign Of Catalyst

lives the t'w"Msea ,1 1.1 0 l@0 an 1.6 * 10?r golfs 0sibefwe'fl

-10-

catalyst/min., for EE' and E'E', respectively. The rate for E'E' is thus

about 16 times that for E'. Whether or not the relatively modest rate

increase for E'E' is due to the operation of the special, metallacyclic

rachanism is questionable.

It was also observed that the following catalyst precursors all gave the

sam turnover nubers after the initial abrupt drop: L3RhCl, (acac)Rh(ethylene)2

and Rh2 (CO) 4 C12 . This suggests that the final catalytic species are Identical.

The redistribution products of pentamnthyldislloxane (EE') are shown

in Table It. The mjor product Is E'E which most likely comes from an

exchange of trimthylsiloxy for mthyl on EE' (eq. 7). The unsymmetric

2 r ififb 2 N - He3SiOS1IH(H)OSlN3 + NO SiH (7)

S (EE') (ED'E)

mature of CE' also reveals that SiO/SiO exchanges must occur, e.g., eq. 8.

2 IOsOSlNs, '. (b35s1)2o + (We 2Sl)20 (8)

(E') (EE) (E'E')

The 'U disproportiomates further. In fact, all of the "symmetric"

ollgmers, 'DE1 In Table II most probably result from SiO/SiO exchanges.

I

Table III presents the redistribution products of E'DE'. One of the

mijor products, E'D2 E, is again most probably formed as a result of the

SO1SiO exchange shown in the Table. The other major product is the cyclic

etrinmer, D3 D. If this cyclic forms from an internal exchange (cf. eq. 5),

hee Its precursor is E'DD'DE', the expected first turnover product result-

$no from the SiO/Me exchange shown in the Table. If this scheme is correct,

then the ET'DE must cyclize nearly as fast as it is formed since its

,on,,tration Is extremely low for a Ist turnover product.

£DD'E reacts with 12(C0)ClIr to give a mixture of the metallacycles

b-Ik (R - H3 I0).9 The overall composition is well established by elemental

0 R 0 R0S " I C Me MeSi SiLRL .)I

%%Ir'.. 110N r _1 Ir Si

L ZZO, 0, -: i- 0 ./ I *Si 1r0'N eI M Me L H I R

(3b) (3c)

a.lysi$. No r, the 1H-NMR in the Si-Me region consists of a set of over-

eaisq peaks in three main "bunches" at 6 0.8, 0.6 and 0.2. Five peaks

wid two shoulders are distinguishable. The mixture of isomers 3-5 should

rse a total of eight methyl environments.

.. ...- ML mmmm mm mm . .m i"

-12-

If the redistribution reaction of ED'D'E were to proceed via the pre-

viously proposed metallacycle mechanism, then the primary reaction products

would be given by eq. 9 (R = Me3SiO). The oligomeric siloxanes should

(n+I)ED'D'E + ED'(-T-)nD'E + n RMeSiH 2 (9)

E

have pendant Me3SiO groups along the polymer backbone. The RteSiH 2 should

disproportionate very rapidly to give products, e.g., MeSiH 3(g) and ED'E via

R/H (R = Me3SiO) exchanges. However, the products listed in Table IV are

best rationalized by assuming that both SiO bonds adjacent to the hydrogen-

bearing silicon are labilized, not Just the central Si-O bond as would be

the case if a metallacycle were necessary to cause labilization.

Me MeI

Me3SiO -- Si -'-O - SiOSi Me3SI

H H

In other words, EDjE, upon its interaction with the catalyst, supplies

E, EDi , and ED' groups for exchange with 5i0, Si-e, and Si-H bonds.

The predicted "Ist turnover" products are then given by the following

equations:

-13-

SiO/SiO exchanges:

ED'E - [E, D'E, ED'] - E'E + EDE + EDE (10)2 23 4

SiO/H exchanges:

EDjEED2 'E - [E, DYE, ED'] - E-T-D'E + ET(D'E)2

E (11)

(SisH) (Si6H2)...... E-T--DE5

DE

(Si7H3 )

SiO/Me exchanges:

IIEDE -1 E D #E, ED'J ED2 E > ET'DIE + ETIDI2 2E)24*......E)

E. (Si6H3 )

(Si5H2)

+ ET'O'E (12)ID2'E (Si7H4)

Of the predicted possibilities, EO'E is definitely observed; and Si5H,

S 5H2, two Si6H2 isomers, and an S17H3 isomer are observed. These may possibly

correspond to the underlined species in eq. 10-12. The remaining species can

all be rationalized as "2nd turnover" products resulting from E/H, ED'/H,

ED/H. etc. exchanges on the "lst turnover" products. It is interesting to note

-14-

that the Si H isomer of possible structure, ED'[T(E)]20'E, is a "2nd

turnover" product according to this scheme, but has the second highest

concentration of any product. This same phenomenon occurs in the Rh-

catalyzed redistribution of E'E' wherein the "2nd turnover" product, E'D2E'

has a higher concentration than the supposed "1st turnover" product, E'DE'

(see Fig. 1). In any event, the metal complex catalyzed redistribution

of EDgE leads to a very complex mixture, the composition of which is con-

sistent with the notion that SiO and Sife bonds adjacent to Si-H bonds are

labilized and undergo exchange reactions.

Finally, we note that the metal species which are formed in the presence

of Si-H bonds are sufficiently active to activate the C-H bond of benzene

to subs-tutteby Si. 10 As shown in Tables I and II, various phenyl sub-

st'tuted siloxanes and silanes are produced along with the rearrangement

products. That the benzene solvent is the source of these phenyl groups in

the case of iridium catalysts was demonstrated by using C6D6 as the solvent.

The resulting phenyl-containing products are d5-substituted and their

fragmentation patterns are entirely consistent with their being ds-phenyl

groups.5

SUMARY

Siloxanes having at least one Si-H bond undergo redistribution reactions

in the presence of certain transition metal complexes, especially those of

Pt, Pd, Ir and Rh. The observed products are formed as a result of scrambling

all the groups attached to the silicon bearing the hydrogen atom; and, to a

much lesser extent, as a result of more common SiO/SiO exchanges as observed

-15-

with acid or base catalyzed rearrangements.lbll It appears that with the

transition metal catalysts, SiO/Me and SiO/H exchanges are faster than

SiO/SiO exchanges, so that these redistributions compliment the classical

acid or base catalyzed redistributions. Synthetically useful rates and

selectivities have been achieved recently by supporting the iridium complexes

on high surface area oxides.12

The nature of the metal-silyl species involved in the catalytic cycle

is unclear, although several possibilities have been discussed in some

detail.lb Likely intermediates are mono- and dinuclear silylene complexes

and complexed silanones. The remarkable stability of appropriately substituted

silylenes has been demonstrated recently,13 and silanones are commonly

postulated as intermediates. 4 . . . . .

ACKNOWLEDGEMENTS

The authors thank the Office of Naval Research for support of this work.

A gift of dimethylchlorosilane from the Dow Corning Corporation is gratefully

acknowledged, as is a loan of precious metals from Johnson atthey, Inc.

The GC-Mass Spectrometer was purchased with the aid of NSF Grant No.

CHE77-11338.

4

-16-

REFERENCES

1. Part IV of Netal-Complex Catalyzed Redistribution Reactions of

Organosilanes". Other papers in this series: (a) Part 1I; W. A.

Gustavson, P. S. Epstein, and H. 0. Curtis, Organomtallics (submitted);

(b) Part 11: H. D. Curtis and P. S. Epstein, Adv. Organomtal. Che. 19

(1981) 213-255; (c) Part 1: M. 0. Curtis and J. Greene, J. Am. Chm. Soc.

100 (1978) 6362.

2. The abbreviated notation for silicones used here is as follows:

E (end group) - H&3 Sl01 2 , 0) (difunctional) a He SlO2 / 2 ; T (trifunctional)

HiS0 3/ 2 . A primed letter indicates a substitution of hydrogen for methyl

(i.e., 0' - HMeSiO2 / 2 ), and a superscript "P Indicates substitution ofP

phenyl for methyl (e.g., EP * PhN&2SIO1/ 2-). For example:

Ne3SiOSiMe2H - EE'; PhMe 2 SiOSIM2 OSiMe 2H - EP DE'; (He3SiO)3StH - E3To, etc.

3. H. D. Curtis, J. Greene and W. H. Butler, J. Organomtal. Chem. 164

(1979) 371.

4. S. Sokolow, J. Karnofsky, P. Gustafson, "INCOS Data System", Finnigan

Application, Report No. 2, 1978, Finnegan Corporation, Sunnyvale, CA.

S. A detailed account of the identification of organosiloxanes by combined

electron impact - (EIMS) and chemical ionization mass spectrometry

(CIPS) will be given elsewhere: H. 0. Curtis and P. S. Epstein, to be published.

6. J. E. Coutant and R. J. Robinson, Ch. 12 in *Analysis of Silicones",

A. L. Smith, Ed., John Wiley and Sons, New York, NY, 1974.

7. K. Vrieze, J. P. Collman and C. T. Sears, norg. $yn., 11 (1968) 101.

8. J. A. Osborne, F. H. Jardine, J. F. Young, and G. Wilkinson, J. Chem. Soc. A

1966, 1711.

-17-

9. The disiloxane, (HOz?eSi)20 (6z-benzyl). also gives a mixture of cis-

and trans-metallacycles with L2Pt: L. G. Bell, W. A. Gustavson and

1. 0. Curtis, submitted for publication.

10. W. A. Gustavson, P. S. Epstein and N. 0. Curtis, Organometallics,

. (1962) 000.

11. 0. R. Veyenber, L. 6. Malone, Od W. H. Atell, Ann. N.Y. Acad. Sc.

159 (1969) 38.

12. W. A. Gustavsen and N. 0. Curtis, to be submitted.

13. a) R. Mst, N. J. Fink and J. Nichl, Science, 214 (1981) 1343;

b) S. Nasamune, Y. Hanzawa, S. NIrekaml, T. Bally, and J. F. Blount,

J. A. Chem. Soc., 104 (1962) 1150.

14. a) C. N. oltno, i. 0. Bush, D. N. Roark, and L. H. Soner,

J. Oroanometal. Chem., 66 (1974) 29; (b) T. J. Barton and 3. A. Kilgour,

J. Am. Chem. Soc., 96 (1976) 7231; (c) D. Seyfrth, T. F. 0. Lim,

and 0. P. Duncan, 3. Am. Chem. Soc., 100 (1978) 1626.

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