Site-Directed Anchoring of an N-Heterocyclic Carbene on a Dimetal Platform: Evaluation of a Pair of Diruthenium(I) Catalysts for Carbene-Transfer Reactions from Ethyl Diazoacetate

Site-directed anchoring of naphthyridine-functionalized N-heterocylic carbene (NHC) is achieved on a metal−metal singly bonded diruthenium(I) platform. Room-temperature treatment of 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (PIN·HBr) with Ru 2 (CH 3 COO) 2 (CO) 4 in acetonitrile affords the unsupported compound Ru 2 (CO) 4 (κ 2 C 2,N 1 -PIN) 2 Br 2 ( 1 ). Judicious alteration in the NHC ligand resulted in the bridged compound Ru 2 (CO) 4 (CH 3 COO)(μ 2 -κ 2 C 2,N 1 -BIN)Br ( 2 ) (BIN = 1-benzyl-3-(3-phenyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene). X-ray analysis revealed the chelate binding of PIN on each ruthenium at equatorial sites for 1, and the bridge-chelate binding of BIN spanning the diruthenium core for 2 . The catalytic utilities of the BAr F (tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) salts of these compounds are evaluated toward carbene-transfer reactions from ethyl diazoacetate including aldehyde olefination, cyclopropanation, and X−H (X = O, N) insertions. 1-BAr F is clearly shown to be the superior catalyst. DFT calculations are undertaken to understand the influence of NHC binding on the electronic structures of the “Ru 2 (CO) 4 ” core and to rationalize the lower activity of 2-BAr F .