A Unifying Bonding Concept for Metal Hydrosilane Complexes

Abstract

Experimental and theoretical charge density studies and molecular orbital analyses suggest that the complexes [Cp2Ti(PMe3)SiH2Ph2] (1) and [Cp2Ti(PMe3)SiHCl3] (2) display virtually the same electronic structures. No evidence for a significant interligand hypervalent interaction could be identified for 2. A bonding concept for transition-metal hydrosilane complexes aims to identify the true key parameters for a selective activation of the individual M-Si and Si-H bonds.

Conciliatory Inductive Model Explaining the Origin of Changes in the η2-SiH Bond Length Caused by Presence of Strongly Electronegative Atoms X (X = F, Cl) in Cp(OC)2Mn[η2-H(SiH3–nXn)] (n = 0–3) Complexes

“…As already mentioned in Introduction, there are several theoretical models aimed at explaining the trans effect, 10,14,16,17,20 some of them are briefly mentioned at present. As early as in 1990 Lichtenberger and Rai-Chaudhuri 10 proposed that the presence of a highly electroneg-…”

“…Therefore, from this point of view, the trans position at -SiR 3 is unique in Cp(OC) 2 Mn[η 2 -H(SiH 3−n X n )] and similar complexes. 2 We have very recently shown 18 that, contrary to the well-known elongation of the η 2 -SiH bond caused by the presence of a halogen atom being trans to this bond, [15][16][17][18] halogens at other positions lead, instead, to the shortening of this bond. Thus, we have shown that the length of the η 2 -SiH bond in Cp(OC) 2 Mn[η 2 -H(SiH 3−n X n )] results from two opposite effects, i.e.…”

“…8). This peculiarity is due to the fact that the electronegative atom (or subsitutent) in the trans position to the η 2 -SiH bond particularly activates this bond [15][16][17][18] making it specifically long. Therefore, from this point of view, the trans position at -SiR 3 is unique in Cp(OC) 2 Mn[η 2 -H(SiH 3−n X n )] and similar complexes.…”

“…It should be noted that, although there are many models (see the Results and discussion section for their brief presentation) introduced to explain either the trans effect 10,14,16,17,20 or the somewhat surprising almost constant length of the η 2 -SiH bond regardless of the number of chlorine atoms at HSiR 3 , 12,15 none of these models, if used individually, explains all of the observed changes in the η 2 -SiH bond length (i.e., the findings that the length of the…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] This, at least partly, results from the fact that the Mn· · · (η 2 -SiH) unit can present various binding motifs, from the one where the hydrogen atom belonging to the HSiR 3 moiety is still strongly bonded to silicon to the situation corresponding to considerable separation of H and Si atoms, i.e., to a fully oxidatively added silane. Moreover, the intermediate stages, as the saying goes "at the arrested degree of oxidative addition", are not uncommon at all.…”