Nucleophilic carbenes bond distances

Ru—C(carbene) bond distances are shorter than Ru—P bond lengths, but this can simply be explained by the difference in covalent radii between P and The variation of Ru—C(carbene) bond distances among ruthenium carbene complexes illustrates that nucleophilic carbene ligands are better donors when alkyl, instead of aryl, groups are present, with the exception of 6. This anomaly can be explained on the basis of large steric demands of the adamantyl groups on the imidazole framework which hinder the carbene lone pair overlap with metal orbitals. Comparison of the Ru—C(carbene) bond distances among the aryl-substituted carbenes show... 

Nucleophilic carbene 4 (R = Me, R = H) has been shown to disrupt the polymeric structure of beryllium dichloride to form an ionic carbene complex, 10 (15). The crystal structure of 10 revealed that the cation possesses a distorted tetrahedral coordination geometry at the beryllium center. The average Be-Cl bond distance (2.083(7) A) is... 

Reaction of a stable carbene with iodine results in compound 46, which can be considered an isolated transition state which models the nucleophilic attack of the carbene on the iodine molecule (Scheme 25).55 The iodine-iodine bond js significantly lengthened and the carbon iodine bond distance of 2.104(3) A is slightly elongated when compared to that of iodoarenes. The authors report that protic solvents promote ionic dissociation to the 2-iodoimidazolium ion which is isoelectronic with the tellerium adduct 44. 

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