Cycloheptatrienyl Zirconium Sandwich Complexes with Lewis Basic Phospholyl Ligands (Phosphatrozircenes): Synthesis, Structure, Bonding and Coordination Chemistry

The transmetalation reaction between [(η 7 ‐C 7 H 7 )ZrCl(tmeda)] ( 1 ; tmeda= N , N , N ′, N ′‐tetramethylethylenediamine) and various phospholide anions leads to a new class of mixed sandwich complexes: [(η 7 ‐C 7 H 7 )Zr(η 5 ‐C 4 PMe 4 )] ( 2 ), [(η 7 ‐C 7 H 7 )Zr(η 5 ‐C 4 PH 2 Me 2 )] ( 3 ) and [(η 7 ‐C 7 H 7 )Zr(η 5 ‐C 4 PPhHMe 2 )] ( 4 ). The presence of Lewis basic phosphorus atoms and Lewis acidic zirconium atoms allows ambiphilic behaviour to be observed, and X‐ray diffraction analysis reveals dimeric arrangements for 2 and 3 with long intermolecular ZrP bonds, whereas 4 remains monomeric in the solid state. DFT calculations indicate that the metal–phosphorus interaction is weak, and accordingly, complexes 2 – 4 act as monodentate ligands upon reaction with [W(CO) 5 (thf)]. The resulting complexes [W(CO) 5 (L)] 5 – 7 (L= 2 – 4 ) were studied by IR spectroscopy and compared with the [W(CO) 5 ] complex 9 , containing the phosphane‐functionalised trozircene [(η 7 ‐C 7 H 7 )Zr(η 5 ‐C 5 H 4 PPh 2 )] ( 8 ). They all show a close resemblance to simple phosphanes, such as PMe 3 , although molecular orbital analysis of 2 reveals that the free electron pair in the phosphatrozircenes is not the HOMO. Four equivalents of 2 can replace 1,4‐cyclooctadiene (COD) in [Ni(cod) 2 ] to form the homoleptic, distorted tetrahedral complex [Ni{ 2 } 4 ] ( 10 ).