Phosphinoalkylsilyl Complexes. 12. Stereochemistry of the Tridentate Bis(diphenylphosphinopropyl)silyl (biPSi) Framework:  Complexation That Introduces “Face Discrimination” at Coordinatively Unsaturated Metal Centers. X-ray Crystal and Molecular Structures of Pt[SiMe(CH2CH2CH2PPh2)2]Cl, IrH[SiMe(CH2CH2CH2PPh2)2]Cl, and RuH[SiMe(CH2CH2CH2PPh2)2](CO)2 1

• Published in: Organometallics 1997-12, Vol.16 (26), p.5669-5680
• Main Authors: Brost, Ron D, Bruce, Gregg C, Joslin, Frederick L, Stobart, Stephen R
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om970518k

Reaction of the bis(phosphinoalkyl)silanes RSiH[(CH2) n PR1 2]2 (R = Me or Ph, n = 2 or 3, R1 = Ph or Cy, i.e., cyclohexyl; biPSiH for R = Me, n = 2, R1 = Ph) with Pt(COD)Cl2 (COD = cycloocta-1,5-diene), [Ir(COD)Cl]2, trans-M(PPh3)2(CO)Cl (M = Rh or Ir), or Ru3(CO)12 affords products that are complexes of tridentate biPSi silyl analogues, in which the Si center is anchored through attachment of trans P atoms at the transition-metal site. The platinum(II) compounds Pt[SiMe(CH2CH2PPh2)2]Cl (1), Pt[SiMe(CH2CH2PCy2)2]Cl (2), Pt[SiPh(CH2CH2PCy2)2]Cl (3), Pt[SiPh(CH2CH2PPh2)(CH2CH2PCy2)]Cl (4), Pt[SiMe(CH2CH2CH2PPh2)2]Cl (5), Pt[SiMe(CH2CH2CH2PCy2)2]Cl (6), and Pt[SiPh(CH2CH2CH2PPh2)2]Cl (7), which have been characterized by 1H, 13C, and 31P 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)2Si(Cl)Me]Cl (8,8‘) in which the two P atoms are also trans. The five-coordinate, 16e, d6 Ir(III) 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 stereoisomers (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(biPSi)(CO)SnCl3 (12 and 13). Treatment of 10 and 11 (3:1) with LiAlH4 yields 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 hydride ligands are nonequivalent and show 2 J HH cis = 5.1, 4.4 Hz, 2 J HH trans ≈ 0, respectively. Similar treatment with LiAl2H4 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, d6 Ru(II) homologues RuH[SiMe(CH2CH2PPh2)2](CO)2 (17) and RuH(biPSi)(CO)2 (18) are formed in sealed-tube reactions at elevated temperature but in very poor yields. NMR spectroscopy suggests that in solution the biPSi backbones of 2−7 and 9−13 are equivalent, establishing planar symmetry (point group C s ) perpendicular to the ligand template, although this is not maintained in the solid state as shown crystallographically for compounds 5, 9, 13, and 18. Bond distances trans to Si are long in 5 and 13 (2.44 and 2.66 Å