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

Abstract New mononuclear titanium and zirconium imido complexes [M(NR)(R′ 2 calix)] [M=Ti, R′=Me, R= t Bu ( 1 ), R=2,6‐C 6 H 3 Me 2 ( 2 ), R=2,6‐C 6 H 3 i Pr 2 ( 3 ), R=2,4,6‐C 6 H 2 Me 3 ( 4 ); M=Ti, R′=Bz, R= t Bu ( 5 ), R=2,6‐C 6 H 3 Me 2 ( 6 ), R=2,6‐C 6 H 3 i Pr 2 ( 7 ); M=Zr, R′=Me, R=2,6‐C 6 H 3 i Pr 2 ( 8 )] supported by 1,3‐diorganyl ether p‐tert‐ butylcalix[4]arenes (R′ 2 calix) were prepared in good yield from the readily available complexes [MCl 2 (Me 2 calix)], [Ti(NR)Cl 2 (py) 3 ], and [Ti(NR)Cl 2 (NHMe 2 ) 2 ]. The crystallographically characterised complex [Ti(N t Bu)(Me 2 calix)] ( 1 ) reacts readily with CO 2 , CS 2 , and p ‐tolyl‐isocyanate to give the isolated complexes [Ti{N( t Bu)C(O)O}(Me 2 calix)] ( 10 ), [{Ti(μ‐O)(Me 2 calix)} 2 ] ( 11 ), [{Ti(μ‐S)(Me 2 calix)} 2 ] ( 12 ), and [Ti{N( t Bu)C(O)N(‐4‐C 6 H 4 Me)}(Me 2 calix)] ( 13 ). In the case of CO 2 and CS 2 , 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(C 7 H 8 ) 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‐C 6 H 4 Me)(Me 2 calix)] ( 14 ), [Ti(N‐4‐C 6 H 4 Fc)(Me 2 calix)] ( 15 ) [Fc=Fe( η 5 ‐C 5 H 5 )( η 5 ‐C 5 H 4 )], and [{Ti(Me 2 calix)} 2 {μ‐(N‐4‐C 6 H 4 ) 2 CH 2 }] ( 16 ). Reaction of 1 with H 2 O, H 2 S and HCl afforded the compounds [{Ti(μ‐O)(Me 2 calix)} 2 ] ( 11 ), [{Ti(μ‐S)(Me 2 calix)} 2 ] ( 12 ), and [TiCl 2 (Me 2 calix)] in excellent yields. Furthermore, treatment of 1 with two equivalents of phenols results in the formation of [Ti(O‐4‐C 6 H 4 R) 2 (Me 2 calix)] (R=Me 17 or t Bu 18 ), [Ti(O‐2,6‐C 6 H 3 Me 2 ) 2 (Me 2 calix)] ( 19 ) and [Ti(mbmp)(Me 2 calix)] ( 20 ; H 2 mbmp=2,2′‐methylene‐bis(4‐methyl‐6‐ tert ‐butylphenol) or CH 2 ({CH 3 }{C 4 H 9 }C 6 H 2 ‐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‐C 6 H 4 R)(Mecalix)} 2 ] [R=Me ( 23 ) or t Bu ( 24 )] where Mecalix=monomethyl ether of p‐tert‐ butylcalix[4]arene. The products of the rearrangement reaction are [Ti(O‐4‐C 6 H 4 Me) 2 ( paco ‐Me 2 calix)] ( 25 ) and [Ti(O‐4‐C 6 H 4 t Bu) 2 ( paco ‐Me 2 calix)] ( 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 crystallographically characterised. Complexes with sterically more demanding phenolate ligands, namely 19 and 20 and the analogous zirconium complexes [Zr(O‐4‐C 6 H 4 Me) 2 (Me 2 calix)] ( 21 ) and [Zr(O‐2,6‐C 6 H 3 Me 2 ) 2 (Me 2 calix)] ( 22 ) do not rearrange. Density functional calculations for the model complexes [M(OC 6 H 5 ) 2 (Me 2 calix)] with the calixarene possessing either cone or partial cone conformations are briefly presented.