(PHOSPHINOALKYL)SILYL COMPLEXES .10. FORMATION OF CHELATED BIS[(DIPHENYLPHOSPHINOETHYL)DIORGANOSILYL]PLATINUM(II) COMPLEXES - PRECOORDINATION THROUGH PHOSPHORUS, INTERMEDIACY OF A PLATINUM(IV) DISILYL, AND DIASTEREOISOMERISM AT PLANAR PLATINUM(II) IN CHELATE-ASSISTED HYDROSILYLATION

Addition or the silane PPh2CH2CH2SiMe2H (chelH, 1a) to Pt(COD)2 (COD = cycloocta-1,5-diene) affords in high yield the cis-bis chelate Pt(chel)2 (2); formation of the same product from Pt(COD)(X)Y (X = Y = Me; X = Me, Y = Cl) has been shown by NMR spectroscopy (H-1, P-31, Pt-195) to proceed via prior coordination of chelH through P to afford Pt(chelH)2(X)(Y) (cis and trans isomers) and through intermediacy of PtH(chel)2Cl (22) in which P trans to Si at Pt(IV) leads to an exceptionally low 2J(Pt-P) = 1084 Hz. Cleavage of Pt-Si bonds in 2 by HCI can bc controlled to give the monochelate species Pt(chel)(chelH)Cl (7), from which chelH is displaced by PMe2Ph, or trans-PtH(PPh2CH2CH2SiMe2Cl)2Cl (9). Products related to 9 result from Pt-Si bond cleavage by I2 or MeI. Using the analogue Pph2CH2CH2SiMe(Ph)H (1c) of 1a, the analogue Pt[PPh2CH2CH2SiMe(Ph)]2 (4) of 2 is obtained as a mixture of meso and racemic diastereomers in which the latter predominates, as is established by its separation and then reaction with optically pure (+)-2-methylbutyl iodide to give two diastereomeric products of Pt-Si bond cleavage as well as by single-crystal X-ray diffraction.