Prepn: Hieber, Lagally, Z. Anorg. Allg. Chem. 251, 96 (1943); McCleverty, Wilkinson, Inorg. Synth. 8, 211 (1966); Colton et al., Aust. J. Chem. 23, 1351 (1970); Cramer, Inorg. Synth. 15, 14 (1974). Structure: Dahl et al., J. Am. Chem. Soc. 83, 1761 (1961).