Pentamethylcyclopentadienylrhodium complexes with tripod tetradentate ligands and bidentate ‘mixed’ ligands

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Abstract
The synthesis and properties of the complexes [{Rh(C5Me5)}3Cl5L]Y [Y = Cl, BF4, or PF6], obtained from [Rh2(C5Me5)2Cl4] and the appropriate tripodal tetradentate ligands, L = N(CH2CH2PPh2)3 or P(CH2CH2PPh2)3, are reported. These monoligand trimetallic compounds contain two Rh(C5Me5)Cl2 units each bound to a terminal phosphorus atom of the tripod ligand and a Rh(C5Me5)Cl group linked to the third terminal phosphorus and to the apical donor atom, nitrogen for N(CH2CH2PPh2)3, phosphorus for P(CH2CH2PPh2)3. The Rh(C5Me5)Cl group in the N(CH2H2PPh2)3 derivative undergoes substitution when treated with tetrabutylammonium chloride to give [{Rh(C5Me5)Cl2}3{N(CH2CH2PPh2)3}]. The influence of steric factors in the substitution reaction has been investigated by synthesising and characterising the complexes [Rh(C5Me5)Cl{R′2N(CH2)nPR2}]BPh4(n= 2, R = Ph or C6H11, R′= H, Me, or Et; n= 3, R = Ph, R′= H, Me, or Et; R = C6H11, R′= H or Me). The bidentate mixed ligands R′2N(CH2)nPPh2(n= 2, R′= Et; n= 3, R′= Me or Et) give complexes of formula [Rh(C5Me5)Cl{R′2N(CH2)nPPh2}2]BPh4, in which the ligands are monodentate through the phosphorus atom. The crystal structure of [Rh(C5Me5)Cl{Et2N(CH2)2PPh2}2]BPh4 has been determined by X-ray crystallographic analysis. The complexes [Rh(C5Me5)Cl{R′2N(CH2)nPPh2}2]BPh4(n= 2, R′= Et; n= 3, R′= Me) exist as four rotamers due to restricted rotations of the bulky phosphine substituents about the Rh–P bonds, as shown by low-temperature 31P n.m.r. spectroscopy.

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