1. This review covers the literature of 1976 but also includes selected references from late 1975 and early 1977. While every effort has been made to include all pertinent references, there undoubtedly are inadvertent omissions and we apologize in advance to those authors involved. Because of the unavailability of many journals at the time of preparation of this review, Chemical Abstracts is the sole source for several references – those references are so indicated by inclusion of the appropriate CA citation number.
2. Most abbreviations used in this article are standard, as for example tabulated in the third edition of Cotton and Wilkinson's “Advanced Inorganic Chemistry” Interscience, N. Y., 1972. Additional abbreviations are as follows: OAc = acetate anion, triphos = Ph-P(CH2CH2PPh22, diphos = Ph2PCH2CH2PPH2
3. J. A. Siegel and E. Deutsch, ibid., 311.