Cationic Group 4 Metallocene–(o‐Phosphanylaryl)oxido Complexes: Synthetic Routes to Transition‐Metal Frustrated Lewis Pairs

Synthetic routes to cationic group 4 metallocene–( o ‐phosphanylaryl)oxido compounds of the type [Cp R 2 M(OPR 2 )][WCA] (M = Ti, Zr, Hf; WCA = weakly coordinating anion) are described. The neutral mono‐methyl complexes [Cp R 2 ZrMe(OPR 2 )] 1 – 6 [Cp R = Cp ( 1 – 3 ) or Cp* ( 4 ); OPR 2 = o ‐OC 6 H 4 (P t Bu) 2 ( 1 and 4 ), OCMe 2 CH 2 (P t Bu) 2 ( 2 ) or OC(CF 3 ) 2 CH 2 (P t Bu) 2 ( 3 )] are prepared by protonolysis of [Cp R 2 ZrMe 2 ] by the parent alcohol. The remaining methyl group in such complexes is best removed by protonolysis with [DTBP][B(C 6 F 5 ) 4 ] (DTBP = 2,6‐di‐ tert ‐butylpyridinium) to yield the desired cationic complexes 7 and 8 in the case of 1 and 4 . In the case of 2 and 3 , this method leads to side reactions. Treatment with B(C 6 F 5 ) 3 yields the desired cations in all cases; however, side reactions with the generated [MeB(C 6 F 5 ) 3 ] anion in subsequent reactions leads to problems. Hafnium analogues may be synthesised by similar routes. In the case of titanium, a different method must be adopted: chloride abstraction using [Et 3 Si][B(C 6 F 5 ) 4 ] from the parent complex [Cp 2 TiCl(OPR 2 )]. Such cationic group 4 metallocene–( o ‐phosphanylaryl)oxido compounds exhibit reactivity that is best described by the frustrated Lewis pair concept.