Isolable dicarbon stabilized by a single phosphine ligand

Reactive Dicarbon as a Flexible Ligand for Transition-Metal Coordination and Catalysis

“…Intriguingly, the observed C(1)–C(2) bond length in the carbenoid ligand slightly contracted to 1.217 (3) Å than its free form (1.237 (4) Å), which we attributed to a further delocalization of its second lone pair residing on C α into a C2 moiety, as the coordination of metal complex lowers the electron density of C β . This structural finding further validates the notion that 4C with a double carbene character appears as the major electronic resonance form, as identified by previous computational analysis . The trans -Rh–CO bond (Rh(1)–C(59), 1.910(3) Å) is substantially longer than the cis- carbonyl bond (Rh(1)–C(58), 1.826(3) Å), which is due to the stronger trans- influence exerted by ligand 4 .…”

“…13 The X-ray crystal structure and spectroscopic characteristics of free form 4 have been determined in our previous report. 10 Reactivity studies in combination with quantum chemical analysis, as previously reported, suggested that the two carbon atoms of the L → C2 complex both have a carbene-like character. This motivated the exploration of 4 as a robust, electron-rich ligand to coordinate to metal centers.…”

“…Deprotonation of 3a / b was achieved using an equimolar strong base KHMDS to afford phosphine-stabilized dicarbon 4 . The X-ray crystal structure and spectroscopic characteristics of free form 4 have been determined in our previous report . Reactivity studies in combination with quantum chemical analysis, as previously reported, suggested that the two carbon atoms of the L → C2 complex both have a carbene-like character.…”

“…This structural finding further validates the notion that 4C with a double carbene character appears as the major electronic resonance form, as identified by previous computational analysis. 10 The trans-Rh−CO bond (Rh(1)−C(59), 1.910(3) Å) is substantially longer than the cis-carbonyl bond (Rh(1)−C(58), 1.826(3) Å), which is due to the stronger transinfluence exerted by ligand 4. Interestingly, the average bond length for rhodium carbonyl (Rh−CO) in 5 is shorter than that for known NHC rhodium complexes, 15 which is consistent with the IR measurement for TEP values that ligand 4 has enhanced σ-donating strength compared to NHCs and CAAcs.…”

“…Later, a bis remote N-heterocyclic carbene (rNHC)-supported dicarbon complex was reported by Kinjo et al 8 Thereafter, Uchiyama and co-workers reported that hypervalent trimethysilylethynyl-substituted-λ3-iodane could serve as a synthetic precursor to generate transient dicarbon under conventional laboratory conditions. 9 Most recently, our group reported the synthesis of an isolable monophosphine adduct of dicarbon, 10 which further demonstrated unprecedented chemical reactivity.…”