Reductive Activation Of Tripod Metal Compounds: Identification Of Intermediates And Preparative Application

[tripodCOCl(2)] {tripod = CH3C(CH2PPh2)(3)} when treated with KC8 in THF solution under an argon atmosphere produces a reactive species ["tripodCo(0)''] (A) which undergoes oxidative additions with stannanes, [tripodCo(H)(2)(SnBu3)] (4), formed, for example, by addition of Bu3SnH. Silanes, R3SiH, undergo the same type of reaction producing [tripodCo(H)(2)(SiR3)] (R = Et: 5a; R = Ph: 5b). The solid-state structures of all the compounds [tripodCo(H)(2)(ER3)] (E = Si, R = Ph; E = Sn, R = Ph, Bu) are rather similar. While they contain six-coordinate cobalt with the formal oxidation state of cobalt being +III the coordination geometry is not octahedral: the heteroelement E deviates from the position which it would have in octahedral coordination by around 40 degrees while the other five ligands, three phosphorus and two hydrogen, have the expected interligand angles of around 90 degrees and 180 degrees, respectively. The deviation of the heteroelement E is such that it approaches the metal bonded hydrogen atoms leading to short H center dot center dot center dot E contacts of only about 190 pm (E = Si) and 230 pm (E = Sn), respectively, The generation of a reactive species ["tripodCo(0)''] (A) was transferred to the synthesis of a reactive tripodnickel(0) species by treating a THF solution of [(DME)NiBr2] with KC8 in the presence of tripod. This species reacts with two electron donor ligands L to produce the pseudo tetrahedral compounds [tripodNi(L)] {L = PPh3 (6), AsPh3 (7), cHexNC (8), tBuNC (9), C2H4 (10)}. The identity of the reactive nickel(0) species as unequivocally deduced from NMR experiments is [tripod(4)Ni(3)] (12). All compounds were characterised by the usual analytic techniques including X-ray analysis where applicable. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).