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Issue 3, 2015
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Reactions of heteroallenes with cyclam-based Zr(IV) complexes

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Abstract

This work describes reactions of heteroallenes with diamido–diamine cyclam-based Zr(IV) complexes of the general formula (Bn2Cyclam)ZrX2 (X = OtBu, 1, OiPr, 2, SPh, 3, NHtBu, 14) as well as the di-orthometallated species ((C6H4CH2)2Cyclam)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–Namido bonds of the cyclam to the heteroallene (4–9). DFT calculations showed that κ2-N,N′-ureate bonding is favoured over κ2-N,O-ureates, which in turn may be formed in reactions with bulky isocyanates as 1-naphthyl isocyanate (NpN[double bond, length as m-dash]C[double bond, length as m-dash]O). The reactions of 2 with N,N′-cyclohexylcarbodiimide (CyN[double bond, length as m-dash]C[double bond, length as m-dash]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 C1 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[double bond, length as m-dash]C[double bond, length as m-dash]O) also proceeds through insertion, involving one Zr–NHtBu bond. However, it was observed that the reaction of (Bn2Cyclam)Zr(NHtBu)2, 14, with MesN[double bond, length as m-dash]C[double bond, length as m-dash]O follows a different path if the reaction is carried out at 60 °C. In this case the reaction leads to [2 + 2] addition of the Zr–Ncyclam bond to the isocyanate, with a concomitant occurrence of orthometallation of the one benzyl pending group of the cyclam ring. The reaction of tBuN[double bond, length as m-dash]C[double bond, length as m-dash]O with the di-orthometallated complex ((C6H4CH2)2Cyclam)Zr, 17, also gave a κ2-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.

Graphical abstract: Reactions of heteroallenes with cyclam-based Zr(iv) complexes

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Publication details

The article was received on 16 Sep 2014, accepted on 11 Nov 2014 and first published on 12 Nov 2014


Article type: Paper
DOI: 10.1039/C4DT02851A
Citation: Dalton Trans., 2015,44, 1441-1455
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    Reactions of heteroallenes with cyclam-based Zr(IV) complexes

    L. G. Alves, F. Madeira, R. F. Munhá, S. Barroso, L. F. Veiros and A. M. Martins, Dalton Trans., 2015, 44, 1441
    DOI: 10.1039/C4DT02851A

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