Synthesis and Reactivity of Calix[4]arene-Supported Group 4 Imido Complexes

New mononuclear titanium and zirconium imido complexes [M(NR)(R′2calix)] [M=Ti, R′=Me, R=tBu (1), R=2,6‐C6H3Me2 (2), R=2,6‐C6H3iPr2 (3), R=2,4,6‐C6H2Me3 (4); M=Ti, R′=Bz, R=tBu (5), R=2,6‐C6H3Me2 (6), R=2,6‐C6H3iPr2 (7); M=Zr, R′=Me, R=2,6‐C6H3iPr2 (8)] supported by 1,3‐diorganyl ether p‐tert‐butylcalix[4]arenes (R′2calix) were prepared in good yield from the readily available complexes [MCl2(Me2calix)], [Ti(NR)Cl2(py)3], and [Ti(NR)Cl2(NHMe2)2]. The crystallographically characterised complex [Ti(NtBu)(Me2calix)] (1) reacts readily with CO2, CS2, and p‐tolyl‐isocyanate to give the isolated complexes [Ti{N(tBu)C(O)O}(Me2calix)] (10), [{Ti(μ‐O)(Me2calix)}2] (11), [{Ti(μ‐S)(Me2calix)}2] (12), and [Ti{N(tBu)C(O)N(‐4‐C6H4Me)}(Me2calix)] (13). In the case of CO2 and CS2, the addition of the heterocumulene to the TiN multiple bond is followed by a cycloreversion reaction to give the dinuclear complexes 11 and 12. The X‐ray structure of 13⋅4(C7H8) clearly establishes the N,N′‐coordination mode of the ureate ligand in this compound. Complex 1 undergoes tert‐butyl/arylamine exchange reactions to form 2, 3, [Ti(N‐4‐C6H4Me)(Me2calix)] (14), [Ti(N‐4‐C6H4Fc)(Me2calix)] (15) [Fc=Fe(η5‐C5H5)(η5‐C5H4)], and [{Ti(Me2calix)}2{μ‐(N‐4‐C6H4)2CH2}] (16). Reaction of 1 with H2O, H2S and HCl afforded the compounds [{Ti(μ‐O)(Me2calix)}2] (11), [{Ti(μ‐S)(Me2calix)}2] (12), and [TiCl2(Me2calix)] in excellent yields. Furthermore, treatment of 1 with two equivalents of phenols results in the formation of [Ti(O‐4‐C6H4R)2(Me2calix)] (R=Me 17 or tBu 18), [Ti(O‐2,6‐C6H3Me2)2(Me2calix)] (19) and [Ti(mbmp)(Me2calix)] (20; H2mbmp=2,2′‐methylene‐bis(4‐methyl‐6‐tert‐butylphenol) or CH2({CH3}{C4H9}C6H2‐OH)2). The bis(phenolate) compounds 17 and 18 with para‐substituted phenolate ligands undergo elimination and/or rearrangement reactions in the nonpolar solvents pentane or hexane. The metal‐containing products of the elimination reactions are dinuclear complexes [{Ti(O‐4‐C6H4R)(Mecalix)}2] [R=Me (23) or tBu (24)] where Mecalix=monomethyl ether of p‐tert‐butylcalix[4]arene. The products of the rearrangement reaction are [Ti(O‐4‐C6H4Me)2 (paco‐Me2calix)] (25) and [Ti(O‐4‐C6H4tBu)2(paco‐Me2calix)] (26), in which the metallated calix[4]arene ligand is coordinated in a form reminiscent of the partial cone (paco) conformation of calix[4]arene. In these compounds, one of the methoxy groups is located inside the cavity of the calix[4]arene ligand. The complexes 24, 25 and 26 have been crystallographical