Dialkylcarbamato Complexes of Ni(II), Zn(II), and Cd(II)–Tetraazacycloalkanes Obtained from CO2-Uptake, and X-Ray Structure of (Diethylcarbamato)((7RS,14RS)5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane)nickel(II) Perchlorate

Nickel(II), zinc(II), and cadmium(II) complexes of certain tetraazacycloalkanes (L), [M(L)](ClO4)2, take up CO2 as R2NCO2− to give carbamato complexes, [M(O2CNR2)(L)]+, where L=(7RS,14RS)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L1) for M=Ni2+, and L=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L2) for M=Ni2+, Zn2+, and Cd2+. The resulting complexes have been characterized by means of IR, and NMR or electronic spectroscopy. X-Ray analysis of [Ni(O2CN(C2H5)2)(L1)]ClO4 (monoclinic C2/c, a=15.842(3), b=13.675(3), c=13.753(2) Å, β=109.94(1)°) shows that it is a discrete six-coordinate complex with cis-NiO2N4 geometry, and the carbamato ligand is bidentate. Desired carbamato complexes were hardly obtained with [M(L)]2+ containing tetraaza macrocyclic ligand which favors square-planar coordination. All the data indicate that carbamate ions chelate the metals, and thus use of tetraazacycloalkanes which fold readily is essential for this type of CO2 uptake.