Imidazol-2-ylidene-N′-phenylureate ligands in alkali and alkaline earth metal coordination spheres - heterocubane core to polymeric structural motif formationElectronic supplementary information (ESI) available: For crystallographic details in CIF. CCDC 1046050-1046056. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt00490j

The synthesis and isolation of two potassium, one lithium and two calcium complexes of imidazol-2-ylidene- N ′-phenylureate ligands [Im R NCON(H)Ph] [(R = t Bu ( 1a ); Mes ( 1b ) and Dipp ( 1c ); Mes = mesityl, Dipp = 2,6-diisopropylphenyl] are described. Potassium complexes, [{κ 2 -(Im Mes NCONPh)K} 4 ] ( 2b ) and [{κ 3 -(Im Dipp NCONPh)K} 2 {KN(SiMe 3 ) 2 } 2 ] n ( 2c ), were prepared in good yields by the reactions of 1b and 1c , respectively, with potassium bis(trimethyl)silyl amide at ambient temperature in toluene. Lithium complex [{(2,6- t Bu 2 -4-Me-C 6 H 2 O)Li(Im t Bu NCON(H)Ph)} 2 {Im t Bu NCON(H)Ph}] ( 3a ) was isolated by a one-pot reaction between 1a and LiCH 2 SiMe 3 , followed by the addition of 2,6- t Bu 2 -4-Me-C 6 H 2 OH in toluene. Calcium complex [{κ 2 -(Im t Bu NCONPh)Ca{N(SiMe 3 ) 2 }-{KN(SiMe 3 ) 2 }] n ( 4a ) was isolated by the one-pot reaction of 1a with [KN(SiMe 3 ) 2 ] and calcium diiodide in THF at ambient temperature. The solid-state structures of ligand 1a and complexes 2b , 2c , 3a and 4a were confirmed by single-crystal X-ray diffraction analysis. It was observed that potassium was coordinated to the oxygen atom of urea group and to the nitrogen atom of the imidazolin-2-imine group, in the solid-state structure of 2b . In complex 4a , the calcium ion was ligated to the monoanionic imidazol-2-ylidene- N ′-phenylureate ligand in a bi-dentate (κ 2 ) fashion through the oxygen and nitrogen atoms of the isocyanate building block leaving the imidazolin-2-imine fragment uncoordinated. In the solid state of the potassium complex 2c , tri-dentate (κ 3 ) coordination from the imidazol-2-ylidene- N ′-phenylureate ligand was observed through the oxygen and nitrogen atoms of the isocyanate building block and of the imidazolin-2-imine fragment. In contrast, in the dimeric lithium complex 3a , the neutral imidazol-2-ylidene- N ′-phenylureate ligand was bound to the lithium centre in a mono-dentate fashion (κ 1 ) through an oxygen atom of the isocyanate moiety. It is to be noted that in each complex thus observed, the elongated carbon-nitrogen bond distances indicate substantial electron delocalisation from the imidazole ring to the ureate group present in ligand 1 . Synthetic and structural details of imidazol-2-ylidene- N ′-phenylureate ligand supported two potassium complexes with a hetero-cubane K 4 O 4 core and a polymeric structure, along with a mixed metal Ca-K complex are presented.