N-alkyl functionalised expanded ring N-heterocyclic carbene complexes of rhodium(i) and iridium(i): structural investigations and preliminary catalytic evaluationElectronic supplementary information (ESI) available: Structure refinement details for compounds 4, 5, 6, 10 and 14. CCDC 905711905715. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt32823b

A series of new N -alkyl functionalised 6- and 7-membered expanded ring N -heterocyclic carbene (NHC) pro-ligands 36 and their corresponding complexes of rhodium( i ) and iridium( i ), [M(NHC)(COD)Cl] 714 and [M(NHC)(CO) 2 Cl] 1522 are described. The complexes have been characterised by 1 H and 13 C{ 1 H} NMR, mass spectrometry, IR and X-ray diffraction. It is noted from X-ray diffraction studies that the N -alkyl substituents are found to orientate themselves away from the metal centre due to unfavourable steric interactions resulting in low percent buried volume (% V bur ) values in the solid state. The heterocycle ring size is also found to dictate the spatial orientation of the N -alkyl substituents in the neopentyl functionalised derivatives 10 and 14 . The 7-membered derivative 14 allows for a conformational twist of the heterocycle ring with the N -alkyl substituents adopting a mutually trans configuration with respect to each other, while the more rigid 6-membered system 10 does not allow for this conformational twist and consequently the N -alkyl substituents adopt a mutually cis configuration. The -donor function of this new class of expanded ring NHC ligand has also been probed by measured IR stretching frequencies of the [M(NHC)(CO) 2 Cl] complexes 1522 . A preliminary catalytic survey of the hydrogenation of functionalised alkenes with molecular hydrogen under mild conditions has also been undertaken with complex 10 , affording an insight into the application of large ring NHC ancillary ligands bearing N -alkyl substituents in hydrogenation transformations. The synthesis, structural/electronic evaluation and preliminary catalytic application of N -alkyl functionalised expanded ring NHC complexes of Rh( i ) and Ir( i ) is described.