Osmium hydrido complex anion

The role of protonic acids in the stepwise oxidative addition of five-coordinate complexes is well illustrated by reactions of acids with the osmium(O) complex (XXXV). Hexafluorophosphonic and tetrafluoroboric acids form stable adducts (XXXVla) and (XXXVIb) which have been characterized as 1 1 electrolytes (39, 103). Similar cationic adducts (XXXVIc) have been formed by reaction of Os(CO)3(PPh3)2 with dry HCl and HBr gas [103). The osmium(II) hydrido cation (XXXVI) possesses trans CO groups (marked with an asterisk) which are mutually labilized through the trans effect. In the presence of a nucleophilic conjugate anion such as bromide one of these CO groups is replaced to yield a neutral adduct... 

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