title: Synthesis and Reactivity of Four- and Five-Coordinate Low-Spin Cobalt(II) PCP Pincer Complexes and Some Nickel(II) Analogues.
abstract: Anhydrous CoCl2or [NiCl2(DME)] reacts with the ligand PCPMe-iPr (1) in the presence ofnBuLi to afford the 15eand 16esquare planar complexes [Co(PCPMe-iPr)Cl] (2) and [Ni(PCPMe-iPr)Cl] (3), respectively. Complex2is a paramagnetic d7low-spin complex, which is a useful precursor for a series of Co(I), Co(II), and Co(III) PCP complexes. Complex2reacts readily with CO and pyridine to afford the five-coordinate square-pyramidal 17ecomplexes [Co(PCPMe-iPr)(CO)Cl] (4) and [Co(PCPMe-iPr)(py)Cl] (5), respectively, while in the presence of Ag+and CO the cationic complex [Co(PCPMe-iPr)(CO)2]+(6) is afforded. The effective magnetic moments μeffof all Co(II) complexes were derived from the temperature dependence of the inverse molar magnetic susceptibility by SQUID measurements and are in the range 1.9 to 2.4 μB. This is consistent with a d7low-spin configuration with some degree of spin-orbit coupling. Oxidation of2with CuCl2affords the paramagnetic Co(III) PCP complex [Co(PCPMe-iPr)Cl2] (7), while the synthesis of the diamagnetic Co(I) complex [Co(PCPMe-iPr)(CO)2] (8) was achieved by stirring2in toluene with KC8in the presence of CO. Finally, the cationic 16eNi(II) PCP complex [Ni(PCPMe-iPr)(CO)]+(10) was obtained by reacting complex3with 1 equiv of AgSbF6in the presence of CO. The reactivity of CO addition to Co(I), Co(II), and Ni(II) PCP square planar complexes of the type [M(PCPMe-iPr)(CO)]n(n= +1, 0) was investigated by DFT calculations, showing that formation of the Co species,6and8, is thermodynamically favorable, while Ni(II) maintains the 16econfiguration since CO addition is unfavorable in this case. X-ray structures of most complexes are provided and discussed. A structural feature of interest is that the apical CO ligand in4deviates significantly from linearity, with a Co-C-O angle of 170.0(1)°. The DFT-calculated value is 172°, clearly showing that this is not a packing but an electronic effect.
authors.affiliation: Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9, A-1060 Vienna, Austria.
authors.forename: Sathiyamoorthy
authors.initials: S
authors.lastname: Murugesan
authors.affiliation: Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9, A-1060 Vienna, Austria.
authors.forename: Berthold
authors.initials: B
authors.lastname: Stöger
authors.affiliation: Centro de Química e Bioquímica/DQB and Centro de Física da Matéria Condensada, Faculdade de Ciências, Universidade de Lisboa , 1749-016 Lisboa, Portugal.
authors.forename: Maria Deus
authors.initials: MD
authors.lastname: Carvalho
authors.affiliation: Centro de Química e Bioquímica/DQB and Centro de Física da Matéria Condensada, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal; Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal.
authors.forename: Liliana P
authors.initials: LP
authors.lastname: Ferreira
authors.affiliation: Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9, A-1060 Vienna, Austria.
authors.forename: Ernst
authors.initials: E
authors.lastname: Pittenauer
authors.affiliation: Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9, A-1060 Vienna, Austria.
authors.forename: Günter
authors.initials: G
authors.lastname: Allmaier
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa , Avenida Rovisco Pais No. 1, 1049-001 Lisboa, Portugal.
authors.forename: Luis F
authors.initials: LF
authors.lastname: Veiros
authors.affiliation: Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9, A-1060 Vienna, Austria.
authors.forename: Karl
authors.initials: K
authors.lastname: Kirchner