Iron–iron bonding versus iron–phosphorus bonding in binuclear diphosphacyclobutadiene iron carbonyl complexes

1,3-Diphosphacyclobutadiene as a ligand in binuclear manganese carbonyl derivatives: Role of the ring phosphorus atoms

“…The charges depend on the number of the ligands attached on the manganese atoms. For example, for the manganese atoms bearing three CO groups or two CO groups plus a phosphorus lone pair (in 6S-1 and is for the manganese atom bearing three CO groups plus a phosphorus lone pair.Previous studies on the Wiberg Bond Indices (WBIs) of metal carbonyls such as Fe 2 (CO) 9 and Fe 3 (CO)12 show that the WBI values are relatively low, often only 0.2 to 0.3 for formal metal-metal single bonds[49]. This is also true for the Mn-Mn interactions in the singlet structures discussed in the present paper.Thus the WBI value for the Mn-Mn single bond in 5S-1 is only ~0.2.…”

“…Previous theoretical studies on the binuclear 1,3-diphosphacyclobutadiene iron carbonyls (Me 2 C 2 P 2 ) 2 Fe 2 (CO) n [12] increases the negative charge on the manganese atoms so that they are less receptive to phosphorus coordination through PMn dative bonds.…”

“…In such a configuration a neutral  4 , 1 -R 2 P 2 C 2 ligand functions as a six-electron donor to the pair of metal atoms. In order to assess the effects of the basicity of the ring phosphorus atoms in 1,3-diphosphacyclobutadiene metal carbonyl complexes the structures and thermochemistry of the binuclear 1,3-diphosphacyclobutadiene iron carbonyls (Me 2 C 2 P 2 ) 2 Fe 2 (CO) n (n = 5, 4, 3, 2) were studied by density functional theory [12] for comparison with the corresponding previously studied [13] binuclear cyclobutadiene iron carbonyls (C 4 H 4 ) 2 Fe 2 (CO) n . Methyl rather than the bulkier tert-butyl substituents were used for this study in order to facilitate the optimizations of large numbers of starting structures.…”

Competition between phosphorus lone pairs and ring π-systems in binding to transition metals: Binuclear diphosphacyclobutadiene cobalt carbonyl derivatives

“…In order to evaluate the effects of basicity of the ring phosphorus atoms in 1,3-diphosphacyclobutadiene metal complexes, we have studied the structures and thermochemistry of the binuclear metal carbonyl complexes (Me 2 C 2 P 2 ) 2 M 2 (CO) n (M = Fe [17], Mn [18]; n = 5, 4, 3, 2) complexes using density functional theory for comparison with the corresponding binuclear cyclobutadiene metal carbonyls (C 4 H 4 ) 2 M 2 (CO) n (M = Fe [19], Mn [20]). Methyl rather than tert-butyl ring substituents were used in order to facilitate the calculations.…”

“…However, low-energy structures were found for (Me 2 C 2 P 2 ) 2 Fe 2 (CO) 3 and (Me 2 C 2 P 2 ) 2 Mn 2 (CO) 4 having terminal  4 -Me 2 C 2 P 2 rings with short MM distances indicating the formal triple bonds required to give each metal atom the favored 18-electron configuration. The involvement of the ring phosphorus lone pairs in the 1,3-diphosphacyclobutadiene metal complexes (Me 2 C 2 P 2 ) 2 M 2 (CO) n (M = Fe [17], Mn [18]) of iron and manganese makes the corresponding cobalt derivatives (Me 2 C 2 P 2 ) 2 Co 2 (CO) n of interest. This is particularly true since previous studies on the binuclear phospholyl cobalt carbonyls (C 4 H 4 P) 2 Co 2 (CO) n suggested lack of involvement of the phosphorus lone pairs in the lowenergy structures.…”