PHOSPHINOALKYLSILYL COMPLEXES - 12 - STEREOCHEMISTRY OF THE TRIDENTATE BIS(DIPHENYLPHOSPHINOPROPYL)SILYL (BIPSI) FRAMEWORK - COMPLEXATION THAT INTRODUCES FACE DISCRIMINATION AT COORDINATIVELY UNSATURATED METALCENTERS - X-RAY CRYSTAL AND MOLECULAR-STRUCTURES OF PT[SIME(CH2CH2CH2PPH2)(2)]CL, IRH[SIME(CH2CH2CH2PPH2)(2)]CL, AND RUH[SIME(CH2CH2CH2PPH2)(2)](CO)(2)

Reaction of the bis(phosphinoalkyl)silanes RSiH[(CH2)(n)PR21](2) (R = Me or Ph, n = 2 or 3, R-1 = Ph or Cy, i.e., cyclohexyl; biPSiH for R = Me, n = 2, R-1 = Ph) with Pt(COD)Cl-2 (COD = cycloocta-1,5-diene), [I r(COD)Cl](2), trans-M(PPh3)(2)(CO)Cl (M = Rh or Ir), or Ru-3(CO)(12) a ffords products that are complexes of tridentate biPSi silyl analogues , in which the Si center is anchored through attachment of trans P ato ms at the transition-metal site. The platinum(II) compounds Pt[SiMe(CH 2CH2PPh2)(2)]Cl (1), Pt[SiMe(CH2CH2PCy2)(2)]Cl (2), Pt[SiPh(CH2CH2PCy2 )(2)]Cl (3), Pt[SiPh(CH2CH2PPh2)(CH2CH2PCy2)]Cl (4), Pt[SiMe(CH2CH2CH2 PPh2)(2)]Cl (5), Pt[SiMe(CH2CH2CH2PCy2)(2)]Cl (6), and Pt[SiPh(CH2CH2C H2PPh2)(2)]Cl (7), which have been characterized by H-1, C-13, and P-3 1 NMR spectroscopy, possess distinguishable square faces with Me on Si projecting in one direction and the buckled (CH2)(n) backbones in the other. Cleavage of the Pt-Si bond in Pt(biPSi)Cl (5) by HCl affords a pair of diastereomers HPt[(PPh2CH2CH2CH2)(2)Si(Cl)Me]Cl (8,8') in whi ch the two P atoms are also trans. The five-coordinate, 16e, d(6) Ir(I II) complex IrH(biPSi)Cl (9) is isolated as a single diastereomer, but octahedral IrH(biPSi)(CO)Cl is formed as a 3:1 mixture of stereoisome rs (10 and 11, CO or Cl trans to Si, respectively, i.e., H trans to Cl or CO) that react with SnCl2 to afford (also 3:1) the analogues IrH(b iPSi)(CO)SnCl3 (12 and 13). Treatment of 10 and 11 (3:1) with LiAlH4 y ields a diastereomeric pair of cis-dihydrido complexes IrH2(biPSi)(CO) (14,14') (1:3), accompanied by a trans-dihydrido stereoisomer 15 and a fac-biPSi stereoisomer 16 as minor products; in 14, 14' and 15 the h ydride ligands are nonequivalent and show (2)J(HHcis) = 5.1, 4.4 Hz, ( 2)J(HHtrans) approximate to 0, respectively. Similar treatment with (L iAlH4)-H-2 affords monodeuterioisotopomers 14a,14'a, while reaction of compound 9 with LiAlH4 under CO gas initially affords 16 as a single product that subsequently isomerizes to 14,14'. The octahedral, 18e, d (6) Ru(II) homologues RuH[SiMe(CH2CH2PPh2)(2)](CO)(2) (17) and RuH(biP Si)(CO)(2) (18) are formed in sealed-tube reactions at elevated temper ature but in very poor yields. NMR spectroscopy suggests that in solut ion the biPSi backbones of 2-7 and 9-13 are equivalent, establishing p lanar symmetry (point group C-s) perpendicular to the ligand template, although this is not maintained in the solid state as shown crystallo graphically for compounds 5, 9, 13, and 18. Bond distances trans to Si are long in 5 and 13 (2.44 and 2.66 Angstrom, to Cl or SnCl3, respect ively), but in 9 Ir-Cl at 2.30 Angstrom is short, occupying the equato rial plane with Si and H in a distorted TBP structure (Si-Ir-Cl 129 de grees). The M-Si distances are 2.31 (5), 2.29 (9), 2.42 (13), and 2.46 Angstrom (18). In 9 and 13, the H at Ir is anti vs Me on Si (of biPSi ), whereas in 18, the Ir-H and Si-Me bonds are syn.