Synthesis and reactivity of heterodinuclear Fe-Ni complexes with a bridging alkoxysilyl ligand. Crystal structure of [(OC)(3)Fe{mu-Si(OMe)(2)(OMe)}(mu-dppm)NiMe]

The new heterobimetallic complex [(OC)(3)Fe{mu -Si(OMe)(2)(OMe)}(mu -dppm)N iCl] (1) was obtained in 95% yield by reaction of [NiCl2(PPh3)(2)]in THF wi th K[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)] at -78 degreesC. The analogous bromo an d iodo complexes were also obtained; the latter is, however, less stable an d could not be isolated pure. They display the first examples of a bridging alkoxysilyl ligand between Fe and Ni, and the mu (2)-eta (2)-SiO bridge is also present in the methyl complex [(OC)(3)Fe{mu -Si(OMe)(2)(OMe)}(mu -dpp m)NiMe] (4) and its phenyl analogue 5. The presence of the Fe-Si-O --> Ni f our-membered rings was confirmed by a crystal structure determination of 4. Treatment of 1 with excess (allyl)MgCl led to the expected bimetallic ally l complex [(OC)(3){(MeO)(3)Si}Fe(mu -dppm)Ni(eta (3)-C3H5)] (6). The rapid eta (3)-allyl --> eta (1)-allyl --> eta (3)-allyl rearrangement is potentia lly assisted through stabilization of the coordinatively unsaturated Ni cen ter by a SiO --> Ni interaction. The bimetallic benzyl derivative 7 was als o isolated. Purging a THF or benzene solution of 4 at room temperature with CO yielded after a few seconds the acyl complex [(OC)(3)Fe{mu -Si(OMe)(2)( OMe)}(mu -dppm)-NiC(O)Me] (8), which readily decarbonylates. Its reaction w ith norbornadiene leads to the insertion product, which is thought to exist as an isomeric mixture with terminal or chelating acyl group (11 reversibl e arrow 11'). When complex 4 was reacted with (BuNC)-Bu-t, rapid insertion occurred and further coordination of a terminal (BuNC)-Bu-t ligand to Ni le d to the iminoacyl complex [(OC)(3){(MeO)(3)Si}Fe(mu -dppm)Ni{(C((NBu)-Bu-t )Me}((CNBu)-Bu-t)] (12). Complex 1 proved to be a more efficient catalyst ( TON = 4100) for the dehydrogenative coupling of Ph3SnH than its mononuclear counterpart [NiCl2(PPh3)(2)] (TON = 1050). The maximum turnover frequency (TOF) was ca. 9800 h(-1).