Synthesis and reactivity of bis(diphenylphosphino)amine-type ligand cobalt complexes Adam Carrick , Dr. Andrei S. Batsanov, Dr. Dmitry Yufit, Dr. Philip W. Dyer Durham University, UK The coordination chemistry of bis (phosphino) amine-type ligands (RN(PR’ 2 ) 2 ) with cobalt(II) has been scarcely studied, 1 despite the potential application of these complexes as pre-catalysts for olefin oligomerisation (by analogy with their chromium(III) analogues). 2 Here, we show for the first time that ionic cobalt(II) complexes ( e.g. C1a , {E = CH}, X = Cl, Scheme 1 ) containing a Co 2 X 6 2– anion (X = Cl, Br, I, Scheme 1 ) are formed on reaction with RN(PPh 2 ) 2 when R does not contain a suitably positioned Lewis base. In contrast, zwitterionic cobalt(II) complexes ( e.g. C2a , X = Cl, Scheme 1 ) are afforded when R bears a suitably located donor group. Complexes C2a-c are believed to form through initial in situ formation of C1a-c {E = N}, which undergoes intramolecular complexation to afford C2a-c . Operation of this latter pathway is supported by the reaction of C1b ({E = CH}, X = Br) with pyridine, which yields C3 ( Scheme 1 ). Both C1a-c and C2a-c have multiple cobalt(II) centres and so would be difficult to use as well-defined pre-catalysts. Hence, complexes C4a-b , containing only the cationic cobalt(II) centre present in C1a-c and C2a-c , have been synthesised and reduced to form cationic cobalt(I) complexes C5a-b (the active species for olefin oligomerisation 3 ). Finally, zwitterionic cobalt-hydride complex C7 with an octahedral cationic cobalt(III) centre has been synthesised, providing a route for the selective addition of a hydride ligand to the cationic cobalt(II) of C2a .
Scheme 1. The synthesis of complexes C1a-f (where C1d-f are in situ intermediates in the synthesis of C2a-c), C2a-c, C3, C4a-b, C5a-b and C6 from compounds L1 and L2. References
1. C. Fliedel et al ., Inorg. Chem ., 2015 , 54 , 6457 – 6559. 2. S. Sa et al ., J. Mol. Catal. A: Chem ., 2013 , 378 , 17 – 21. 3. M. Gray et al ., ACS Catal ., 2020 , 10 , 4337 – 4348.
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© The Author(s), 2022
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