Substituted metal carbonyls .27. Synthesis, structures, and metal-metal bonding of a ferrocenylphosphine exo-bridged cluster with two heterometallic triangles, [AuMn2(CO)(8)(mu-PPh(2))](2)(mu-dppf), and a twisted-bowtie cluster, PPN+[Au{Mn-2(CO)(8)(mu-PPh(2))}(2)](-) (dppf=1,1'-bis(diphenylphosphino)ferrocene)

Redox condensation of PPN[Mn-2(CO)(8)(mu-PPh(2))] (1; (PPN = N(PPh(3))(2)) with Au2Cl2(mu-P-P) (P-P = (C(5)H(4)PPh(2))(2)Fe (dppf), Ph(2)PC(2)H(4)PPh(2) (dppe)) gives two hexanuclear Au-Mn clusters [AuMn2(Co)(8)(mu-PPh(2))](2)(mu-P-P) (P-P = dppf, (2), dppe (4)), both of which contain a diphosphine bridging two Mn2Au triangles. Complex 2 is formed via an intermediate, AuCl-(mu-dppf)[AuMn2(CO)(8)(mu-PPh(2))], (3), which was isolated. Bridge cleavage of 2 occurs at thf reflux with PPh(3) and room temperature with P(OEt)(3) to give the triangular clusters [(PR(3)-)-AuMn2(CO)(8)(mu-PPb2)] (R = Ph (5), Oft (6)), respectively. The latter exchange of dppf with P(OEt)3 is reversible in solution. Condensation of 1 with AuCl(SMe(2)) gives an anionic pentanuclear cluster, PPN[Au{Mn-2(CO)(8)(mu-PPh(2))}(2)] (7) Complexes 2 and 7 were structurally characterized by single-crystal X-ray diffractometry; Complex 2, which is centrosymmetric with Fe in dppf at a crystallographic inversion center, consists of a ferrocenylphosphine bridging two heterometallic triangles (Au-Mn = 2.660(1) and 2.776(1) Angstrom; Mn-Mn = 3.049(2) Angstrom). Complex 7 is made up of two planar AuMn2P metallacycles fused at An at an angle of 85.50(4)degrees. With crystallographic C-2 symmetry, a twisted-bowtie skeleton resulted with gold at its center. Both Au-Mn (mean 2.806(1) Angstrom) and (PPh(2)-bridged)Mn-Mn (3.105(2) Angstrom) lengths are significantly longer than those in 2. The Mn-Mn bond of 2 is also significantly longer than that of 1. Fenske-Hall MO calculations on 1, 2, and 7 together with Mn-2(CO)(8)(mu-H)(mu-PPh(2)) (8) and (PPhMe(2))AuMn2(CO)(8)(PPh(2)) (9) indicate that aside from 1, all the complexes, including 2 and 7, give a negative overlap population in the Mn-Mn interactions. The Mn-Mn distance appears to be determined by the strength of the AuMn2 interaction and/or the size of H compared to Au. The weaker Mn-Mn and Au-Mn interactions in 7 (as compared to those in 2 and 9, respectively) are likely to be caused by the absence of Au orbital reinforcement in the direction of the Mna moiety as a consequence of symmetry.