Examination of Metal−Silicon Bonding through Structural and Theoretical Studies of an Isostructural Set of Five-Coordinate Silyl Complexes, Os(SiR₃)Cl(CO)(PPh₃)₂ (R = F, Cl, OH, Me)

Abstract

Os(SiCl3)Cl(CO)(PPh3)2 is prepared by treatment of OsPhCl(CO)(PPh3)2 with excess HSiCl3 and serves in turn as the starting material for the syntheses of three more five-coordinate silyl complexes Os(SiR3)Cl(CO)(PPh3)2 (R = F, OH, Me) via substitution of the chloride groups on silicon. All four compounds were fully characterized, including a single-crystal solid-state structure of each derivative. Carbonyl stretching frequencies decrease and Os−Si bond lengths increase as R changes in the order from F to Cl to OH to Me. Ab initio calculations were performed on the model complexes Os(SiR3)Cl(CO)(PH3)2 (R = F, Cl, OH, Me) to explain the trends observed in the IR and X-ray studies, and the importance of the π-acceptor capacities of the silyl groups are discussed.

The structurally characterised silyl complexes, Os(κ2-S2CNMe2)(SiMeCl2)(CO)(PPh3)2 and Os(κ2-S2CNMe2)(SiCl3)(CO)(PPh3)2, which have remarkably unreactive Si–Cl bonds

“…It is also less than the corresponding value for the related Os(j 2 -S 2 CNMe 2 )(SiMe 2 Cl)(CO)(PPh 3 ) 2 at 2.4021(11) Å [12]. The Os-Si distance in 2 (2.3449(12) Å ) is shorter than in either Os(j 2 -S 2 CNMe 2 )(SiMe 2 Cl)(CO)-(PPh 3 ) 2 or 1, as would be expected for a trichlorosilyl ligand [2]. The overall trend is that the Os-Si distance decreases with increasing chloride substitution on silicon.…”

“…The IR spectrum of 1 shows m(CO) at 1893(s), 1877 cm À1 , the observation of two bands presumably arising from solidstate splitting. The IR spectrum of 2 shows m(CO) at 1901(s) cm À1 , this higher value being expected and attributable to the more electron-withdrawing SiCl 3 group [2]. That the geometry of 1 and 2 is as drawn in Scheme 1 is indicated by the presence of two signals for the methyl groups of the dimethydithiocarbamate ligands (in both the 1 H and 13 C NMR spectra) and the observation of a singlet resonance in the 31 P NMR spectra of these compounds.…”

“…Syntheses and crystal structures of Os(j 2 -S 2 CNMe 2 )-(SiMeCl 2 )(CO)(PPh 3 ) 2 (1) and Os(j 2 -S 2 CNMe 2 )-(SiCl 3 )(CO)(PPh 3 ) 2 (2) As depicted in Scheme 1 the reaction between Os(j 2 -S 2 -CNMe 2 )H(CO)(PPh 3 ) 2 and the two chlorosilanes, HSiMeCl 2 and HSiCl 3 proceeds smoothly to give the corresponding colourless osmium silyl complexes, Os(j 2 -S 2 CNMe 2 )(SiMeCl 2 )(CO)(PPh 3 ) 2 (1) and Os(j 2 -S 2 CNMe 2 )-(SiCl 3 )(CO)(PPh 3 ) 2 (2), respectively, in good yield. The IR spectrum of 1 shows m(CO) at 1893(s), 1877 cm À1 , the observation of two bands presumably arising from solidstate splitting.…”

“…Examples include the syntheses of compounds of the type, L n M-SiR 3Àn X n , where X can be H [1], R [2], OH [3,4], OR [5], SR [6], NR 2 [7], and F [2,8]. However, the reactivity of the Si-Cl bonds in chlorosilyl ligands is variable and in some exceptional cases the Si-Cl bonds are quite unreactive towards hydrolysis.…”

“…We have previously reported all three of the five-coordinate, coordinatively unsaturated derivatives, Os(SiMe 2 Cl)Cl(CO)(PPh 3 ) 2 , Os(SiMeCl 2 )Cl(CO)(PPh 3 )2 , and Os(SiCl 3 )Cl(CO)(PPh 3 ) 2 , are readily hydrolysed (KOH/ H 2 O/THF at room temperature within minutes) to the corresponding osmasilanols, Os[SiMe 2 (OH)]Cl(CO)(PPh 3 ) 2 [12], Os[SiMe(OH) 2 ]Cl(CO)(PPh 3 ) 2 [13], and Os[Si(OH) 3 ]-Cl(CO)(PPh 3 ) 2[2,3]. Replacement of the osmium-bound chloride ligand in Os(SiMe 2 Cl)Cl(CO)(PPh 3 ) 2 by the bidentate dimethyldithiocarbamate ligand to give Os(j 2 -S 2 CNMe 2 )(SiMe 2 Cl)(CO)(PPh 3 ) 2 brings about a marked change in the reactivity of the Si-Cl bond.…”