Effect of Diphosphine Ligands on the Metal Framework of Carbido Heteronuclear Cluster Compounds:  X-ray Structure of [Fe₄Au₂C(CO)₁₂(μ-dppm)]·C₇H₈

Abstract

The reaction of (NEt4)2[Fe6C(CO)16] and (AuCl)2(μ-L) (L = diphosphine) depends on the nature of the diphosphine. Unexpectedly, for L = dppm (dppm = bis(diphenylphosphino)methane), the cluster [Fe4Au2C(CO)12(dppm)] (1) was formed, whereas for L = dppe (dppe = 1,2-bis(diphenylphosphino)ethane) the reaction gave the 14-metal cluster (Et4N)2[{Fe6AuC(CO)16}2(μ-dppe)], in which two Fe6CAu fragments are linked by the bridging ligand. Remarkably, 1 is a skeletal isomer of the previously published [Fe4Au2C(CO)12(PEt3)2].

Iron−Gold (or −Mercury) Carbide Clusters Derived from [Fe6C(CO)16]2-. X-ray Crystal Structures of (NEt4)[Fe6C{AuPPh3}(CO)16] and [Fe4C{AuPPh3}(CO)11(NO)]

“…The whole Fe 4 C fragment is very similar to that found in other known butterflies of this type (see below). The Fe−Au bond distances, 2.820(2) and 2.866(2) Å, are very similar to those found in the related compounds [Fe 4 C{AuPPh 3 }(μ-H)(CO) 12 ] 11a and [Fe 4 CAu 2 (CO) 12 (μ-dppm)] . The value of the Au−C distance, 2.095(9) Å, is also comparable to those found in these complexes and in other compounds with Au−C single bonds …”

“…However, the similarity between the iron and the ruthenium compounds is broken when the reaction of the anions [M 6 C(CO) 16 ] 2- (M = Fe, Ru) with (ClAu) 2 (μ-dppm) is compared. Thus, for M = Ru, the final product was [Ru 6 CAu 2 (CO) 16 (μ-dppm)] while, for M = Fe, the cluster [Fe 4 CAu 2 (CO) 12 (μ-dppm)] was isolated. This example shows the difference in thermodynamic stability between the iron and ruthenium clusters as correspond to metal atoms belonging to the first and second periods, respectively.…”

“…If a second gold unit is added, the MO scheme obtained for [Fe 4 C(CO) 12 ] 2- can also be used to explain the compound structure. In the case of [Fe 4 CAu 2 (CO) 12 (μ-dppm)] (H in Chart ), one Au atom bonds to a hinge iron producing a rotation of the carbonyl ligands around this atom, one of the CO becoming semibridging along the Fe−Fe hinge. The same reorganization was observed in a related compound, [HFe 4 B{AuPPh 3 } 2 (CO) 12 ] …”

Gold–Heterometal Interactions and Bonds

“…Different geometries of the heterometallic core were reported in hexanuclear clusters with Au-Fe [241,305,309,[336][337][338][339][340][341][342][343], Au-Ru [262,264,298,315,324, and Au-Os bonds [327,[365][366][367][368][369]. Common structures feature a trigonal bipyramidal fragment capped by a m 3 -Au(PR 3 ), for example, in (Ph 3 P)AuOs 5 (m-H)(h 6 -C 6 H 6 ) (CO) 12 230 [Au-Os 2.819(2)-3.020(2) Å] [365] or (m-dppe)AuRu 4 Cu(m 3 -H) 2 (CO) 12 231 [Au-Ru 2.823(2) Å] [345].…”

“…A class of hexanuclear clusters is based on a butterfly framework of iron or ruthenium atoms m 4 -connected by a carbon [305,324,336,[347][348][349][350] or boron [337-341, 351, 352] atom. In some AuRu 5 (m 5 -C) compounds a Ru-containing moiety (Ru, C,Ru)-connected to the wingtip metal atoms, while the Au(PPh 3 ) bridges the hinge Ru atoms [347][348][349], as in (Ph 3 P)AuRu 5 (m 5 -C)(h 5 -Cp)(CO) 13 243 [Au-Ru 2.780(1)/ 2.750(1) Å] [353].…”