Reversible hydrosilane addition to pyridines enabled by low-coordinate Ca() and Yb() hydrides

The reactions of amides [ t Bu 2 CarbAr 2 ]MN(SiMe 3 ) 2 (THF) (M = Ca ( 5 ), Yb ( 6 )) and [ t Bu 2 CarbAr 2 ]MN(SiMe 3 ) 2 (M = Ca ( 7 ), Yb ( 8 )) coordinated by a bulky carbazolyl ligand ( t Bu 2 CarbAr 2 = 3,6-di- tert -butyl-1,8-bis(3,5-di- tert -butylphenyl)-carbazolyl) with PhSiH 3 allowed for the synthesis of isolable low-coordinate hydrides {[ t Bu 2 CarbAr 2 ]MH(THF)} 2 (M = Ca ( 11 ), Yb ( 12 )) and {[ t Bu 2 CarbAr 2 ]MH(η 6 -C 7 H 8 )} 2 (M = Ca ( 11 ), Yb ( 12 )) featuring dimeric structures. Hydrides 11 and 12 , as well as amides 7 and 8 , proved to be efficient catalysts for PhSiH 3 addition to pyridines at ambient T . However, the same catalyst at 90° C catalyzes the opposite reaction: the release of the parent silane and the restoration of the aromatic pyridine system. Low-coordinate dimeric Ca( ii ) and Yb( ii ) hydrides {[ t Bu 2 CarbAr 2 ]MH(THF)} 2 and {[ t Bu 2 CarbAr 2 ]MH(η 6 -C 7 H 8 )} 2 efficiently catalyze PhSiH 3 addition to pyridines at ambient T . At 90° C the same complex catalyzes the reverse reaction.