Cyclometalation of dialkylbis(triethylphosphine)platinum(II) complexes: formation of Pt,Pt-bis(triethylphosphine)platinacycloalkanes
Cyclometalation of dialkylbis(triethylphosphine)platinum(II) complexes: formation of Pt,Pt-bis(triethylphosphine)platinacycloalkanes
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二烷基双(三乙基膦)铂(II)络合物的环金属化：形成Pt,Pt-双(三乙基膦)铂环烷烃
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发表时间：
1982
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通讯作者：
G. Whitesides
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作者：
R. Dicosimo;S. S. Moore;A. Sowinski;G. Whitesides
The thermal decompositions of three analogues of bis(triethylphosphine)dineopentylplatinum(lI) (L2Pt[CH2C(CHr)r]z (l))-L2PtlcH2c(cH3)2cH2cH3l2 (3), L2ft[CH2C(CH3)2CH2CH2CH3]z (5), and L2pt[CH2C(CH3)2CH2C(CH3)r]' (7)-have been examined. Compounds 3 and 7 decompose more rapidly than I by a factor of ca. 104 to give as products Pl,Pr-bis(triethylphosphine)-3,3-dimethylplatinacyclohexane (4) and Pt,Pt-bis(triethylphosphine)-3,3,5,5-tetramethylplatinacyclohexane (8), respectively, and I equiv of the corresponding alkane. Compound 5 decomposes at a rate ca. 50 times faster than I to yield Pt,Pt-bis(triethylphosphine)-2,4,4-trimethylplatinacyclopentane (6a), -3-methyl-3-n-propylplatinacyclobutane (6b), and -3,3-dimethylplatinacyclohexane (6c). The conversion of 3 to 4 and 5 to 6a proceeds by dissociation of triethylphosphine, intramolecular oxidative addition of a D carbon-hydrogen bond of one the alkyl groups to platinum, and reductive elimination of alkane. The decomposit ion of L2Pt[CH2CH2C(CHr):]z (1t) proceeds by B-hydride el imination rather than cleavage of a carbon-hydrogen bond and formation of platinacycloalkane. The difference in the free energies of activation for reactions which form fourand five-membered platinacycloalkanes is small (AAG| 4 kcal mol-'); that for reactions which form fourand six-membered rings is smaller (AAG+ 0 kcal mol-t). We identify these values of AAG+ with estimates of the strain energies of these rings, assuming the strain energy of the platinacyclohexane is small. The important conclusion from these studies is that the strain energy of the platinacyclobutane studied here is small ((5 kcal mol-r). Homogeneous reactions which break unactivated aliphatic C-H bonds by oxidative addition to transition metals provide mechanistic information which is useful in understanding catalytic reactions of hydrocarbons.a Well-defined stoichiometric reactions (l) Supported by the National Science Foundation, Grant77ll282 CHE. (2) Chevron Fellow, 1980-1982. (3) NIH Postdoctoral Fellow, 1979-1981. (4) Parshal l , G.W. Acc. Chem. Res.1975,8, 113l17. Clarke, J. K. A. ; Rooney, J. l. Adu. Catal.1975, 25,125-183. Shilov, A. E.; Shteinman, A. A. Coord. Chem. Reu.1977,24,97-143. Shilov, A.E. Pure Appl. Chem. 197t, 50.725-733. Scheme I. Mechanism of Formation of Metalacycloalkanes bv Cvclometalation
