Unusually Weak Metal−Hydrogen Bonds in HV(CO)4(P−P) and Their Effectiveness as H• Donors

The V-H bonds in HV(CO)4(P-P) are unusually weak (55 to 58 kcal/mol). They transfer H* to styrene more rapidly than CpCr(CO)3H does and are effective stoichiometric reagents for the cyclization of appropriate 1,6-dienes.