ABSTRACT
(t-BuPOCOP)MoI(2) (1; t-BuPOCOP = C(6)H(3)-1,3-[OP(t-Bu)(2)](2)) has been synthesized from MoI(3)(THF)(3). Upon reduction of 1 with Na/Hg under dinitrogen molecular nitrogen is cleaved to form [(t-BuPOCOP)Mo(I)(N)](-). The origin of the N atom was confirmed using (15)N(2). Protonation of [(t-BuPOCOP)Mo(I)(N)](-) results in the formation of a neutral species in which it is proposed that the proton has added across the Mo-P bond.
Subject(s)
Coordination Complexes/chemistry , Nitrogen/chemistry , LigandsABSTRACT
The iridium pincer complexes (PCP)IrH(4) (1; PCP = [kappa(3)-1,3-(CH(2)P(t)Bu(2))(2)C(6)H(3)]) and (POCOP)IrH(4) (2; POCOP = [kappa(3)-1,3-(OP(t)Bu(2))(2)C(6)H(3)]) have proven to be effective catalyst precursors for dehydrogenation of alkanes. The complex (POCOP)IrH(2) has also been applied successfully as a catalyst for release of H(2) from ammonia borane. Investigation of the "tetrahydride" forms of these complexes by solution NMR methods suggests their formulation as dihydrogen/dihydride species. This is in contrast to the solid state structure of 1, determined by neutron diffraction (at 100 K), which indicates a compressed tetrahydride structure with only weak H-H interactions. Complex 1 (C(24)H(47)IrP(2)) crystallizes in the space group P4(2), tetragonal, (Z = 2) with a = 11.7006 (19) A, c = 9.7008(27) A, and V = 1328.1(5) A(3). Electronic structure calculations on 1 and 2 indicate that the global minima on the potential energy surfaces in the gas phase are tetrahydride structures; however, the dihydrogen/dihydride forms are only slightly higher in energy (1-3 kcal/mol). A dihydrogen/dihydride species is calculated to be the global minimum for 2 when in solution. The barriers to interconversion between the tetrahydride and dihydrogen/dihydride species are almost negligible.
ABSTRACT
Reaction of NaBH4 with (tBuPOCOP)IrHCl 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) A. Compound 1 crystallizes in the space group P1 (Z = 2) with a = 8.262 (5) A, b = 12.264 (5) A, c = 13.394 (4) A, and V = 1256.2 (1) A(3) (30 K). Complex 1 can also be prepared by reaction of BH3 x 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 H2 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) A, b = 11.1233 (2) A, c = 14.6122 (3) A, and V = 6700.21 (19) A(3) (130 K). Reaction of (tBuPOCOP)IrH2 with 9-borobicyclononane (9-BBN) affords complex 4. Complex 4 displays (1)H NMR resonances analogous to 1 and exists in equilibrium with (tBuPOCOP)IrH2 in THF solutions.
ABSTRACT
In the presence of an iridium pincer complex, dehydrogenation of ammonia borane (H3NBH3) occurs rapidly at room temperature in tetrahydrofuran to generate 1.0 equivalent of H2 and [NH2BH2]5. A metal borohydride complex has been isolated as a dormant form of the catalyst which can be reactivated by reaction with H2.
ABSTRACT
A new ligand conceptually creates two sites reminiscent of beta-diketiminates, and upon deprotonation the salts exist in oligomeric forms with potassium ions linking multiple ligands.
