The hydridoirida-β-diketone [(IrH{(PPh 2 (o-C 6 H 4 CO)) 2 H}) 2 (μ-Cl)][BF 4 ] (2) has been used as a homogeneous catalyst for the methanolysis of ammonia-borane to release up to 3 equivalents of hydrogen in the presence of air. With catalyst loadings as low as 0.2 mol%, ammonia-borane undergoes methanolysis within 6 min at 30°C, with TOF 50% of 320 mol H2 • mol Ir À 1 • min À 1 , or within 80 s at 60°C, with an excellent TOF 50% of 1991 mol H2 • mol Ir À 1 • min À 1 , and maintains its catalytic activity in consecutive runs. Triethylamine-borane fails to undergo methanolysis. Kinetic studies indicate first-order dependence on substrate and on catalyst concentration and suggest cleavage of the solvent OÀ H bond being involved in the rate determining step of the reaction. In methanol solution 2 forms cationic [IrH (MeOH){(PPh 2 (o-C 6 H 4 CO)) 2 H}] + (3) and reacts with Me 3 NÀ BH 3 to afford a hydridoirida-β-diketone [IrH(Me 3 NBH 3 ){(PPh 2 (o-C 6 H 4 CO)) 2 H}] + (4), with the borane adduct η 1 -coordinated to iridium. Compound [4][BAr F 4 ] shows dynamic behaviour in solution due to exchange of bridging and terminal BÀ H bonds. A multinuclear NMR study of the catalyzed reaction shows the formation of two ammonia-methoxyborane adduct intermediates, H 3 NÀ BH 2 (OCH 3 ) and H 3 NÀ BH(OCH 3 ) 2 , and an iridium species proposed of the hydridodiacyl type [IrH (H 3 NBH 3À x (OCH 3 ) x )(PPh 2 (o-C 6 H 4 CO)) 2 ] with a coordinated borane adduct. On account of experimental evidence, a simplified catalytic cycle is suggested for the methanolysis of AB to release hydrogen.
One-electron oxidation of palladium(0) and platinum(0) bis(phosphine) complexes enables isolation of a homologous series of linear d 9 metalloradicals of the form [M(PR 3 ) 2 ] + (M = Pd, Pt; R = tBu, Ad), which are stable in 1,2difluorobenzene (DFB) solution for >1 day at room temperature when partnered with the weakly coordinating [BAr F 4 ] − (Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ) counterion. The metalloradicals exhibit reduced stability in THF, decreasing in the order palladium(I) > platinum(I) and PAd 3 > PtBu 3 , especially in the case of [Pt(PtBu 3 ) 2 ] + , which is converted into a 1:1 mixture of the platinum(II) complexes [Pt(PtBu 2 CMe 2 CH 2 )(PtBu 3 )] + and [Pt(PtBu 3 ) 2 H] + upon dissolution at room temperature. Cyclometalation of [Pt(PtBu 3 ) 2 ] + can also be induced by reaction with the 2,4,6-tri-tert-butylphenoxyl radical in DFB, and a common radical rebound mechanism involving carbon-to-metal H-atom transfer and formation of an intermediate platinum(III) hydride complex, [Pt(PtBu 2 CMe 2 CH 2 )H(PtBu 3 )] + , has been substantiated by computational analysis. Radical C−H bond oxidative addition is correlated with the resulting M II −H bond dissociation energy (M = Pt > Pd), and reactions of the metalloradicals with 9,10dihydroanthracene in DFB at room temperature provide experimental evidence for the proposed C−H bond activation manifold in the case of platinum, although conversion into platinum(II) hydride derivatives is considerably faster for [Pt(PtBu 3 ) 2 ] + (t 1/2 = 1.2 h) than [Pt(PAd 3 ) 2 ] + (t 1/2 ∼ 40 days).
The synthesis and iridium coordination chemistry of a new pyridine-based phosphinito pincer ligand 2,6-(ArF2PO)2C5H3N (PONOP-ArF; ArF = 2-(CF3)C6H4) is described, where the P-donors have ortho-trifluoromethylphenyl substituents. The iridium(III) 2,2′-biphenyl (biph)...
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