Stabilization of Niobium(0) and Tantalum(0) in Mixed Metal Clusters containing Silver Atoms

Abstract

Clusters with supporting bridge ligands are rare among Group 5 metals, the only crystallographically established example being [Cp,Nb,(CO),]['] (Cp = q5-C,H,). On the other hand, halo-, 0x0-, and sulfido-bridged clusters of vanadium, niobium and tantalum in oxidation states higher than I are well documented in the literature.L2I Vanadinm(0) compounds are readily accessible,[31 whereas niobium(0) and tantalum(0) complexes mostly have to be prepared by metal vapori~ation.'~' Among the mixed metal clusters [((PPh,)-Au),V(CO),] has been prepared and structurally characterized,l5! while a positive oxidation state for niobium has been foundLb1 in [{(PPh,)Au),Nb(C,H,R),]@.We now wish to report the first structurally characterized carbonyl clusters containing niobium and tantalum in the formal zero oxidation state.The reactions of 1 (dmpe = 1,2-bis(dimethylphosphino)ethane) with silver salts of poorly coordinating anions, namely AgNO, and AgBF,, in THF at room temperature afford compounds of analytical composition 2 [Eq. (a)].The solid state structures of 2 were established by single crystal X-ray diffraction methods.''] Both compounds are isotypic, as shown by Gandolfi photographs of the single crystals used for subsequent intensity measurements.The complexes 2 are structurally related to the osmium" 2] and iron-platinum[' raft-like clusters. The ten non-hydrogen atoms in the asymmetric unit are arranged around the intersection of a crystallographic threefold axis with three twofold axes, i.e. the point symmetry of the resulting molecule is D,, the three silver atoms and the three Group 5 metal atoms lying in the plane containing the twofold axes (Fig. 1).The arrangement of the metal atoms in almost equilateral triangles corresponds to that of a (1 11) plane in a closepacked metal structure, the intermetallic angles being all close to 60". The almost identical Ag-Ag distances of 2.842 A in 2a and 2b are shorter than in silver metal (2.883 In the intermetallic cubic Laves phase NaAg,, which contains a network of corner-connected Ag, tetrahedra, the Ag-Ag distances are 2.810Moreover, a AgAg distance of 2.994(6) A has been in the heterometallic cluster [Pt,Ag,Cl,(C,F,),J20.The distances between Ag and Nb or Ta in 2 a and 2 b are also very similar (2.888 A) and might be compared with the sum of the metallic radii (2.91 A['41).

Altering Charges on Heterobimetallic Transition‐Metal Carbonyl Clusters

“…Neutral clusters like the hypothetical [Ag 3 {M(CO) 6 } 3 ]-related to the trimer [AgM(CO) 4 (dmpe)] 3 [37] -were inaccessible.R ather decomposition was observed when using an equimolar ratio of the startingm aterials. All syntheses were carried out at À35 8C, close to the melting point of the solvent4 FB (m.p.…”

“…[36] In thesec omplexes, niobiumo rt antalumh exacarbonylates serve as ligands for the silver atoms. For group 5e lements, structurally characterized heterometallic clusters are yet limitedt oo nly af ew heteroleptic complexes.T he neutralt rimer [AgM(CO) 4 (dmpe)] 3 (dmpe = 1,2-bis(dimethylphosphino)ethane, M = Nb,T a) [37] appears to be the closest literature reference to the compounds in this work.…”

Intramolecular d10–d10 interactions in heterometallic clusters of the transition metals

“…The first structurally characterized carbonyl clusters of the type [AgM(CO) 4 (dmpe)] 3 (M = Nb, Ta; dmpe = 1,2 bis(dimethylphosphino)ethane) (14) were reported in 1989. 106…”

“…105 The first structurally characterized carbonyl clusters of the type [AgM(CO) 4 (dmpe)] 3 (M = Nb, Ta; dmpe = 1,2 bis(dimethylphosphino)ethane) (14) were reported in 1989. 106 These clusters were isolated from the reaction of Cluster 19 represents a rare example of a neutral Ag-Fe cluster containing phosphines as ancillary ligands for silver.…”

Fausto Calderazzo: Pioneer in Mechanistic Organometallic Chemistry

“…Fausto’s researches on early transition metal carbonyls led to the synthesis of salts containing the hexacarbonyl-niobate and -tantalate anions ([M(CO) 6 ] − ; M = Nb, Ta) under mild conditions (Scheme ) and the stabilization of niobium(0) and tantalium(0) in mixed metal clusters containing silver (Figure ) …”