σ-borane complexes of iridium:: Synthesis and structural characterization

Reaction of NaBH4 with (tBuPOCOP)IrHCI affords the previously reported complex (tBuPOCOP)-IrH2(BH3) (1) (tBuPOCOP = kappa(3)-C6H3-1,3-[OP(tBU)(2)](2)). The structure of 1 determined from neutron diffraction data contains a B-H sigma-bond to iridium with an elongated B-H bond distance of 1.45(5) angstrom. Compound 1 crystallizes in the space group P(1)over bar (Z = 2) with a = 8.262 (5) angstrom, b = 12.264 (5) angstrom, c = 13.394 (4) angstrom, and V= 1256.2 (1) angstrom(3) (30 K). Complex 1 can also be prepared by reaction of BH3 center dot THF with (tBuPOCOP)IrH2. Reaction of (tBuPOCOP)IrH2 with pinacol borane gave initially complex 2, which is assigned a structure analogous to that of 1 based on spectroscopic measurements. Complex 2 evolves H-2 at room temperature leading to the borane complex 3, which is formed cleanly when 2 is subjected to dynamic vacuum. The structure of 3 has been determined by X-ray diffraction and consists of the (tBuPOCOP)Ir core with a sigma-bound pinacol borane ligand in an approximately square planar complex. Compound 3 crystallizes in the space group C2/c (Z= 4) with a = 41.2238 (2) angstrom, b = 11.1233 (2) angstrom, c = 14.6122 (3) angstrom, and V= 6700.21 (19) angstrom(3) (130 K). Reaction of (tBuPOCOP)IrH2 with 9-borobicyclononane (9-BBN) affords complex 4. Complex 4 displays H-1 NMR resonances analogous to 1 and exists in equilibrium with (tBuPOCOP)IrH2 in THF solutions.