Welcoming Neighbour or Inhospitable Host? Selective Second Metal Binding in 5- and 6-Phospha-Substituted Bpy Ligands

Abstract

The controlled formation of mixed-metal bimetallics was realised through use of a fac-[Re(CO)₃(N,N'-bpy-P)Cl] complex bearing an exogenous 2,4,6-trioxa-1,3,5,7-tetramethyl-8-phosphaadamantane donor at the 5-position of the bpy. The introduction of gold, silver, and rhodium with appropriate secondary ligands was readily achieved from established starting materials. Restricted rotation about the C_(bpy)-P bond was observed in several of the bimetallic complexes and correlated with the relative steric bulk of the second metal moiety. Related chemistry with the 6-substituted derivative proved more limited in scope with only the bimetallic Re/Au complex being isolated.

Keywords: heterobimetallic complexes; phospha–bpy ligands; rotamers.

Scheme 1

Synthesis of the ligands CgP-5bpy (5L) and CgP-6bpy (6L).

Figure 1

Optimised geometry of 5L^Re (hydrogens omitted for clarity). Light blue = Re; dark blue = N; green = Cl; red = O; orange = P.

Figure 2

Ortep [45] representation of the molecular structure of 5L^Re,Au. Hydrogen atoms and residual solvent have been omitted for clarity. Selected bond lengths (Å) and angles (°): Re1—N1 2.170(5); Re1—N2 2.162(4); Re1—C21 1.925(6); Re1—C22 1.973(6); Re1—C23 1.924(6); Re1—Cl1 2.4483(16); Au1—P1 2.2177(14); Au1—Cl2 2.2786(15); N1—Re1—C23 170.1(2); N2—Re1—C21 171.9(2); Cl1—Re1—C22 176.42(17); P1—Au1—Cl2 179.34(7).

Figure 3

Geometry optimised molecular structure of 6L^Re,Au. Light blue = Re; dark blue = N; green = Cl; red = O; orange = P; yellow = Au.

Figure 4

Ortep [45] representation of the molecular structure of anti-5L^Re,Rh. Hydrogen atoms and residual solvent have been omitted for clarity. Selected bond lengths (Å) and angles (°): Re1—N1 2.173(3); Re1—N2 2.172(3); Re1—C11 1.902(6); Re1—C12 1.910(4); Re1—C13 1.908(5); Re1—Cl1 2.4563(18); Rh1—P1 2.3176(8); Rh1—Cl2 2.3580(8); N1—Re1—C13 171.67(14); N2—Re1—C12 173.15(15); Cl1—Re1—C11 179.1(2); P1—Rh1—Cl2 84.48(3).

Figure 5

Frontier orbitals of 5L^Re,Au. (a) The HOMO (−6.09 eV); (b) the LUMO (−2.66 eV).