Mono and bis carbene neodymium(III) spirocyclic complexes with a cumulene carbon metal structure

Abstract The formation of metal carbon cumulene structures is rare in synthesis chemistry because properties of the carbene carbon and metal must match properly, such as an electron rich PCP carbene and late transition metals containing d, f rich orbitals, or lanthanide metals. In this study, we performed the first step reaction of [Li 2 C(Ph 2 P = NSiMe 3 ) 2 ] ( 1 ) with NdCl 3 in 1:1 M ratio in situ, with subsequent addition of second molar ratio of 1 to the reaction solution to generate bis carbene neodymium organometallic compound of [Nd{C(Ph 2 P = NSiMe 3 ) 2 } 2 ][Li(THF) n ] ( 2 ). The anion of this isolated compound 2 formed a rare linear carbene metal cumulene structure (C Nd = C) demonstrated by crystal structure determination. In order to synthesize a mono carbene neodymium compound with bis(diphenyliminophosphorane)methandiide ( 1 ) to compare its bonding feature to the reactions of [Li 2 C(Ph 2 P = NSiMe 3 ) 2 ] ( 1 ) with NdCl 3 and CpTl in THF, eventually crystal structure analysis showed that generated another neodymium organometallic complexes of [Cp 2 Nd{CH(Ph 2 P = NSiMe 3 ) 2 } 2 ] ( 3 ), unexpected the methandiide carbon of PCP ligand was protonated. Furthermore, DFT calculations demonstrated the presence of multiple bonding interaction in the carbon metal cumulene structure (C Nd = C). NBO analysis revealed that the average overall C Nd double bond contains 21.19% carbon and 14.43% Nd component respectively, indicating it is a covalent conjugated multiple bonding system. To the best of our knowledge, it is the first structural example of PCP carbene neodymium compound with the cumulene structure (C Nd = C) unit.