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.

(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.

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.

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.

H2 & Co.: A new pincer complex of CoII has been synthesized. Reduction of this complex in the absence of additional ligands results in the formation of a highly reactive mercury‐bridged dicobalt species (1). Subsequent introduction of H2 at low temperature allows the observation of a rare dihydrogen complex of Co (2). Co blue, P yellow, O red, Hg dark gray.

A pair of POCOP-supported mono-and dicarbonyl complexes of Co have been prepared and crystallographically characterized. The reactivity of ( tBu POCOP)Co(CO) with H 2 , acids, and carbon monoxide has been compared to that of the previously reported Rh and Ir counterparts. Co is found to share reactivity traits with both Rh and Ir.

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A new ligand conceptually creates two sites reminiscent of β-diketiminates, and upon deprotonation the salts exist in oligomeric forms with potassium ions linking multiple ligands.Sterically demanding β-diketiminate ligands have come into wide use as tools for forming lowcoordinate inorganic and organometallic complexes. 1 In many cases multimetallic complexes or intermediates are formed that have interesting properties. For example, zinc β-diketiminate complexes catalytically copolymerise 2 We CO 2 and epoxides through a bimetallic mechanism. have reported the cleavage of N-N single bonds and N=N double bonds using diiron(II) complexes. 3,4 One way of understanding these bimetallic reactions is to create dinucleating ligands incorporating multiple β-diketiminate units. 5One conceptually can fuse two β-diketiminate groups by attaching two deprotonated enamines to a heterocycle such as pyridazine or phthalazine. Other workers have reported dinucleating ligands based on these scaffolds. 6 Following this strategy, 1,4-dichlorophthalazine was treated with four equivalents of a deprotonated t-butyl methyl imine precursor to give 1,4-bis-(2-(2,6-diisopropylphenylimino)-3,3-dimethylbutyl)-phthalazine (1, Scheme 1). † It is necessary to use four equivalents because the deprotonated imine is a strong enough base to deprotonate the product. The imine byproduct may be recovered through distillation.The molecular structure of 1 is shown in Fig. 1. The bond distances in 1 are consistent with a C1-C2 single bond and a C1=N1 double bond: this molecule exists as the imine tautomer shown in Scheme 1 rather than the enamine tautomer that predominates in the β-diketimines. 7 The 1 H NMR spectrum of 1 includes a singlet corresponding to four hydrogen atoms on C2 per molecule, and no N-H peak is observed. This suggests that if the enamine/imine or bisenamine tautomers of 1 exist in solution they are minor species. To test whether the minor tautomer is formed, a solution of 1 in THF-d 8 with a drop of D 2 O was sonicated for several days at room temperature. Proton NMR spectroscopy showed no decrease in the integration for the methylene protons, indicating that the hydrogen atom on C2 does not exchange with solvent. We conclude that enamines are not formed under these conditions.Correspondence to: Patrick L. Holland. † 1: Under an atmosphere of N 2, a slurry of lithiated imine was prepared according to ref. 9 (159 mmol in 250 mL pentane) and cooled to −55 °C. A solution of 1,4-dichlorophthalazine (7.93 g, 39.8 mmol) in THF (300 mL) was added dropwise, and the mixture was warmed to room temperature and stirred overnight. The solution was quenched with aqueous HCl (0.08 M, 100 mL). The organic phase was dried over Na 2 SO 4 and concentrated to a sticky orange solid, which was dissolved in hot toluene (250 mL) and cooled to −20 °C. The light yellow solid was isolated by filtration and rinsed with cold hexanes. Yield: 15.17 g, 59%; mp 249 °C; Elem. Anal. C, 81.9; H, 9.4; N, 8.6 (C 44 H 60 N 4 requires C, 81.9; H, 9.4 NIH-PA Aut...