Reactivity of Novel N,N′-Diphosphino-Silanediamine-Based Rhodium(I) Derivatives

The coordination abilities of the novel N,N′-diphosphino-silanediamine ligand of formula SiMe2(NtolPPh2)2 (SiNP, 1) have been investigated toward rhodium, and the derivatives [RhCl(SiNP)]2 (2), [Rh(SiNP)(COD)][BF4] (3), and Rh(acac)(SiNP) (4) have been synthesized. The stability of the dinuclear frame of [RhCl(SiNP)]2 (2) toward incoming nucleophiles has been shown to be dependent on their π-acceptor ability. Indeed, the mononuclear complexes RhCl(SiNP)(L) (L = CO, 5; CNtBu, 6) have been isolated purely and quantitatively upon reaction of 2 with CO and CNtBu, respectively. Otherwise, PPh3 and RhCl(SiNP) equilibrate with Rh(Cl)(SiNP)(PPh3) (7). Carbon electrophiles such as MeI and 3-chloro-1-proprene afforded the oxidation of rhodium(I) to rhodium(III) and the formation of RhCl2(η3-C3H5)(SiNP) (8) and Rh(Me)(I)(SiNP)(acac) (10), respectively. The methyl derivative 10 is thermally stable and does not react either with CO or with CNtBu even in excess. Otherwise, RhCl2(η3-C3H5)(SiNP) (8) is thermally stable but reacts with CO, affording 3-chloro-1-proprene and RhCl(SiNP)(CO) (5). Finally, upon reaction of Rh(acac)(SiNP) (4) and 3-chloro-1-proprene, RhCl(acac)(η1-C3H5)(SiNP) (9a) and [Rh(acac)(η3-C3H5)(SiNP)]Cl (9b) could be detected at 233 K. At higher temperatures, 9a and 9b smoothly decompose, affording the dinuclear derivative [RhCl(SiNP)]2 (2) and the CC coupling product 3-allylpentane-2,4-dione.