Copper hydride clusters of the type (RPNHP) n Cu2n H2n (RPNHP = HN­(CH2CH2PR2)2; n = 2 and 3) have been synthesized from the reaction of (RPNHP)­CuBr with KO t Bu under H2 or in one pot from a 1:2:2 mixture of RPNHP, CuBr, and KO t Bu under H2. With medium-sized phosphorus substituents (R = i Pr and Cy), the phosphine ligands stabilize both hexanuclear and tetranuclear clusters; however, the smaller clusters are kinetic products and aggregate further over time. Use of a bulkier ligand tBuPNHP leads to the formation of only a tetranuclear cluster. Crystallographic studies reveal a distorted octahedral Cu6 unit in ( iPrPNHP)3Cu6H6 (2a) and (CyPNHP)3Cu6H6 (2b), while a tetrahedral Cu4 unit exists in (CyPNHP)2Cu4H4 (2b′) and ( tBuPNHP)2Cu4H4 (2c′), all furnished with face-capping hydrides and bridging RPNHP ligands. The aggregations are maintained in solution, although hydrides are fluxional. These copper clusters are capable of reducing aldehydes and ketones to the corresponding copper alkoxide species. Ranking their reactivity toward N-methyl-2-pyrrolecarboxaldehyde gives 2b′ > 2a, 2b ≫ 2c′, which correlates inversely with the order of thermal stability (against decomposition and cluster expansion).

Synthesis of t BuC≡C(CH 2 ) 4 C≡C t Bu. Under a nitrogen atmosphere, a 1.6 M solution of n BuLi in hexanes (37.5 mL, 60 mmol) was added dropwise to a chilled (−78 °C) solution of tbutylacetylene (4.76 g, 58 mmol) in 60 mL of THF. The resulting mixture was stirred at −78 °C for 20 min and then warmed to room temperature. 1,4-Dibromobutane (3.34 mL, 28 mmol) and hexamethylphosphoramide (HMPA, 20 mL) were added sequentially and the reaction mixture was stirred at room temperature for another 4 h before it was diluted with 100 mL of water. The organic layer was separated and the aqueous layer was extracted with diethyl ether (40 mL × 3).The combined organic layers were dried over Na 2 SO 4 , filtered, and concentrated under vacuum.The diyne product was purified via vacuum distillation (52-56 °C/0.1 mmHg) and isolated as a

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HN(CH2CH2PR2)2-ligated copper borohydride complexes, (RPNHP)Cu(BH4) (R = iPr, Cy, tBu), which can be prepared from (RPNHP)CuBr and NaBH4, are capable of catalyzing the hydrogenation of aldehydes in an alcoholic solvent....