Reactions of heteroallenes with cyclam-based Zr(IV) complexes

This work describes reactions of heteroallenes with diamido-diamine cyclam-based Zr(IV) complexes of the general formula (Bn(2)Cyclam) ZrX2 (X = (OBu)-Bu-t, 1, (OPr)-Pr-i, 2, SPh, 3, (NHBu)-Bu-t, 14) as well as the di-ortho-metallated species ((C6H4CH2) (2)Cyclam) Zr, 17. The reactions of isocyanates or isothiocyanates with 1, 2 or 3 resulted in the formation of N-bonded ureate or thioureate cyclam complexes upon [2 + 2] cycloaddition of the Zr-N-amido bonds of the cyclam to the heteroallene (4-9). DFT calculations showed that. kappa(2)-N,N'-ureate bonding is favoured over. kappa(2)-N,O-ureates, which in turn may be formed in reactions with bulky isocyanates as 1-naphthyl isocyanate (NpN=C=O). The reactions of 2 with N,N'-cyclohexylcarbodiimide (CyN=C=NCy) and carbon disulfide afforded guanidinate and dithiocarbamate fragments, respectively, appended to one of the nitrogen atoms of the cyclam ligand. These reactions represent a reliable method for the synthesis of asymmetrically N-functionalized cyclams giving rise to C-1 symmetry Zr(IV) species by addition of one equivalent of heteroallenes. The reaction of (Bn2Cyclam) Zr(NHtBu) 2, 14, with one equivalent of mesityl isocyanate (MesN=C=O) also proceeds through insertion, involving one Zr-(NHBu)-Bu-t bond. However, it was observed that the reaction of (Bn2Cyclam) Zr(NHtBu) 2, 14, with MesN=C=O follows a different path if the reaction is carried out at 60 degrees C. In this case the reaction leads to [2 + 2] addition of the Zr-N-cyclam bond to the isocyanate, with a concomitant occurrence of orthometallation of the one benzyl pending group of the cyclam ring. The reaction of (BuN)-Bu-t=C=O with the di-orthometallated complex ((C6H4CH2)(2)Cyclam) Zr, 17, also gave kappa(2)-2-N,N'-ureate fragment, by isocyanate addition to the macrocycle. DFT calculations on these systems were conducted in an attempt to rationalise the reactivity patterns observed.