Copper(I) hydride cluster; mild hydride donor in organic synthesis. Prepn and crystal characterization: S. A. Bezman et al., J. Am. Chem. Soc. 93, 2063 (1971); M. R. Churchill et al., Inorg. Chem. 11, 1818 (1972). Improved prepns: D. M. Brestensky et al., Tetrahedron Lett. 29, 3749 (1988); P. Chiu et al., ibid. 44, 455 (2003). Use in reduction of α,β-unsaturated carbonyl compds: W. S. Mahoney et al., J. Am. Chem. Soc. 110, 291 (1988); W. S. Mahoney, J. M. Stryker, ibid. 111, 8818 (1989); in hydrosilylation of aldehydes and ketones: B. H. Lipshutz et al., J. Organomet. Chem. 624, 367 (2001). Brief review: A. de Fátima, Synlett 2005, 1805-1806 (2005).