NMe 2 ), shows a thiolato group transfer involving P-S bond formation between the
central phosphorus atom and a thiolate group, which is also induced by the coordination of a π-acidic CO ligand. According to the preliminary kinetic experimental
data, this reaction reveals a pseudo-first-order decay with respect to the consumption
of 33-SAr under the excess CO(g) conditions, indicating an intramolecular reaction
pathway. When the reaction mixture was exposed to vacuum, a CO ligand was
decoordinated from a Ni(0) center allowing to regenerate a Ni(II)-SAr species. This
result suggests the conversion of a Ni(II) species to a Ni(0) species is fully reversible.
Finally, cooperative reactivity of (PP
SAr P)Ni(CO) (36) occurring between P and Ni
was recognized, when 36 was treated with triphenylmethyl chloride resulting in the
formation of (PPP)Ni-Cl and Ph 3 CSPh as shown in Fig. 16. The corresponding
reaction involves the MLC of a (PPP)Ni scaffold, because the corresponding
thiolato group transfer occurs at a P site via the cleavage of a P-S bond to give a
newly formed C-S bond and concomitantly two-electron oxidation occurs at a nickel
(0) center [40]. We also found that the metal-ligand cooperative group transfer can
compete with migratory insertion reaction [41]. When a nickel(II)-isopropoxide
species reacts with a π-acidic ligand, two different products were detected, presumably due to the polarization of CX bond (X ¼ O or N). When tert-butyl isocyanide
coordinates to 33i PrO, a
i PrO group transfers to the phosphorus atom of a PPP
ligand to generate a phosphinite nickel(0) species (37). Interestingly, with CO(g),
migratory insertion of the
i PrO group occurs to generate an alkoxy carbonyl nickel
(II) species, (PPP)Ni(C(O)O
i Pr) (38; Fig. 16) [41].
The cooperativity of a PPP ligand accompanying a two-electron redox change of
a nickel ion was employed in the activation of CO 2 (Fig. 17) [39]. When a nickel(0)N 2 species, (PP
OMe P)Ni(N 2 ) (39), was exposed to CO 2 (g), the methoxy group of a
Fig. 17 Methoxy group transfer reaction of a (PPP)Ni scaffold involving CO 2 conversion mediated by MLC
Metal-Ligand Cooperativity of Phosphorus-Containing Pincer Systems
87
central phosphorus atom and a thiolate group, which is also induced by the coordination of a π-acidic CO ligand. According to the preliminary kinetic experimental
data, this reaction reveals a pseudo-first-order decay with respect to the consumption
of 33-SAr under the excess CO(g) conditions, indicating an intramolecular reaction
pathway. When the reaction mixture was exposed to vacuum, a CO ligand was
decoordinated from a Ni(0) center allowing to regenerate a Ni(II)-SAr species. This
result suggests the conversion of a Ni(II) species to a Ni(0) species is fully reversible.
Finally, cooperative reactivity of (PP
SAr P)Ni(CO) (36) occurring between P and Ni
was recognized, when 36 was treated with triphenylmethyl chloride resulting in the
formation of (PPP)Ni-Cl and Ph 3 CSPh as shown in Fig. 16. The corresponding
reaction involves the MLC of a (PPP)Ni scaffold, because the corresponding
thiolato group transfer occurs at a P site via the cleavage of a P-S bond to give a
newly formed C-S bond and concomitantly two-electron oxidation occurs at a nickel
(0) center [40]. We also found that the metal-ligand cooperative group transfer can
compete with migratory insertion reaction [41]. When a nickel(II)-isopropoxide
species reacts with a π-acidic ligand, two different products were detected, presumably due to the polarization of CX bond (X ¼ O or N). When tert-butyl isocyanide
coordinates to 33i PrO, a
i PrO group transfers to the phosphorus atom of a PPP
ligand to generate a phosphinite nickel(0) species (37). Interestingly, with CO(g),
migratory insertion of the
i PrO group occurs to generate an alkoxy carbonyl nickel
(II) species, (PPP)Ni(C(O)O
i Pr) (38; Fig. 16) [41].
The cooperativity of a PPP ligand accompanying a two-electron redox change of
a nickel ion was employed in the activation of CO 2 (Fig. 17) [39]. When a nickel(0)N 2 species, (PP
OMe P)Ni(N 2 ) (39), was exposed to CO 2 (g), the methoxy group of a
Fig. 17 Methoxy group transfer reaction of a (PPP)Ni scaffold involving CO 2 conversion mediated by MLC
Metal-Ligand Cooperativity of Phosphorus-Containing Pincer Systems
87