New Heteromultifunctional Fluoroaromatic Bis(phosphinimine) Ligands and Their Complexes. Synthesis and Characterization of New Ligands (Including X-ray Structures of 4,6-(CN)2C6F2-1-(NP(Ph)2CH2PPh2)-3-(NPPh3) and 4,6-(CN)2C6F2-1,3-bis(NP(Ph)2CH2PPh2)) and Their Rhodium(I) Complexes, Including the Structure of the Novel Dimetallic Complex 4,6-(CN)2C6F2-1,3-bis(NP(Ph)2CH2P(Ph)2Rh(CO)Cl)

Abstract

Reaction of 1,3-dicyanotetrafluorobenzene with trimethylsilyl phosphinimines proceeds through stepwise substitution on the fluoroaromatic to yield mono- and ultimately disubstituted derivatives of the form 4,6-(CN)2C6F2-1-A-3-B. Two molar equivalents of a bifunctional phosphinophosphoranimines, Me3SiNP(Ph)2CH2PPh2, result in a dual substitution giving 1 (A = B = (NP(Ph)2CH2PPh2)), whereas 1 equiv of the trimethylsilyl phosphinimine gives the monosubstituted derivative. Treatment of the monosubstituted derivative with a second 1 equiv of the same or a different phosphinimine gives doubly substituted derivatives which can have the same or different phosphorus substituents, e.g. 2, A = (NP(Ph)2CH2P(Ph)2), B = (NPPh3), and 3, A = (NP(Ph)2CH2PPh2), B = (NPPh2Me). Compounds 1, 4,6-(CN)2C6F2-1,3-bis(NP(Ph)2CH2PPh2), and 2, 4,6-(CN)2C6F2-1-(NP(Ph)2CH2PPh2)-3-(NPPh3), have been structurally characterized. In 1, the P(1)N(1) bond length is 1.581(3) Å, the P(3)N(2) bond length is 1.569(4) Å, the P(1)−N(1)−C(6) angle is 132.1(3)°, and the P(3)−N(2)−C(2) angle is 133.2(3)°. For 2, the P(2)N(1) bond length (in the Ph3PN unit) is 1.578(4) Å, the P(3)N(2) bond length in the Ph2PCH2Ph2PN unit) is 1.585(4) Å, the P(2)−N(1)−C(2) angle is 134.7(4)°, and the P(3)−N(2)−C(6) angle is 129.9(4)°. 2 reacted readily with [Rh(CO)2Cl]2 to form the mono metallic chelated Rh complex 4, 4,6-(CN)2C6F2-3-(NPPh3)-1-(NP(Ph)2CH2P(Ph)2Rh(CO)Cl). 1 reacts with both 1 equiv and 0.5 equiv of [Rh(CO)2Cl]2 to form respectively 4,6-(CN)2C6F2-1,3-bis(NP(Ph)2CH2P(Ph)2Rh(CO)Cl), 5, and 4,6-(CN)2C6F2-1,3-bis(NP(Ph)2CH2P(Ph)2)Rh(CO)Cl, 6. The half-metalated complex 6 can be converted to 5 with a second aliquot of the Rh precursor, and the dimetalated complex 5 can be converted to the half-metalated complex 6 by reaction of 5 with more ligand. The bis(phosphine) chelate structure of 6, the dimetalated complex, was deduced from the complex second-order 31P NMR spectrum solved by simulation. The two PIII are trans coordinated to the Rh center, and the two N are not coordinated. There is no PIII−PIII or PV−PV coupling, but each PIII is coupled to two magnetically inequivalent PV. Structural characterization of the dimetalated complex 5 shows a symmetrically substituted complex containing two Rh centers with a square planar geometry around each Rh(I) with the CO cis to the phosphine. Bond angles and lengths are typical for the Rh(I) square planar chelate complex structures. The P(1)−N(1) distance of 1.61(1) Å in the complex is normal for a coordinated iminophosphoranyl group. The directly bound Rh−PIII distance of 2.206(4) Å also lies within the range found in many Rh(I) phosphine complexes of this type.