Dianionic Iron and Ruthenium(2−) Biphosphinine Complexes: A Formal d10 Ruthenium Complex with a Square Planar Geometry

Abstract

Though the Collmans reagent [Fe(CO) 4 ] 2À is probably one of the most popular and useful reagents in organic synthesis, [1] our knowledge of dianionic Group 8 metal complexes still remains limited. In addition to the carbonyl ruthenium analogue [Ru(CO) 4 ] 2À , only a few other complexes are known: the complete series of PF 3 derivatives [M(PF 3 ) 4 ] 2À (M Fe, Ru, Os), [2] the isocyanide complexes [Ru(CNR) 4 ] 2À synthesized by Cooper and co-workers, [3] and the amazing Jonas iron complexes [Fe(C 2 H 4 ) 4 ] 2À and [Fe(cod) 2 ] 2À (cod cycloocta-1,5-diene). [4] We have begun to explore the use of sophisticated phosphinine-based ligands in an effort to design phosphorus equivalents of carbonyl ligands. [5] This we recently illustrated by the successful stabilization of an Au 0 center encapsulated in a silacalix-[4]-phosphinine macrocycle [6] and the synthesis of dianionic 2,2'-biphosphinine complexes of Group 4 [7] and 9 metals. [8] Herein we report the successful stabilization of dianionic Fe and Ru 2,2'-biphosphinine complexes.All our syntheses were carried out using dianion 2 which is readily obtained by reduction of 2,2'-biphosphinine 1 (tmbp) using lithium in excess. [9] Reaction of two equivalents of 2 with one equivalent of [{FeCl 2 (thf) 1.5 } n ] or [Ru(cod)(acac) 2 ] (acac 2,4-pentanedione, acetylacetone) in THF at low temperature, yielded complexes 3 an 4, respectively, which were isolated as highly moisture and oxygen sensitive powders (Scheme 1).The formulation of these two complexes was confirmed by NMR spectroscopic data ( 1 H and 13 C). To gain more structural information, an X-ray crystal structure analysis of complex 4 was carried out (Figure 1). [10] Remarkably, the overall geometry of 4 is not tetrahedral as usually observed for ML 4 d 10 complexes, [8] but square planar; [11] the iron complex 3 is assumed to have the same structure. The two biphosphinines are roughly located in the same plane (V 7.298, V being the interplane angle) and the two cationic [Li(thf) 3 ] units are located above and below the plane in apical positions. Though the structure roughly resembles an octahedron, the Ru´´´Li separation (2.740 (3) ) is long and exceeds the sum of the covalent radii (2.60 ) indicating only a very weak, mainly P P P P Li Li THF THF THF THF THF THF P P M P P 2 a b 2-+ + 3: M = Fe 4: M = Ru 1 2 Scheme 1. Syntheses of 3 and 4: a) Li (excess), THF, 25 8C, 2 h. b) [{FeCl 2 (thf) 1.5 } n ] or [Ru(cod)(acac) 2 ], THF À 80 8C 3RT.Figure 1. Molecular structure of 4. Thermal ellipsoids are set at the 50 % probability level. The hydrogen atoms are omitted for clarity. Important distances [] and angles [8]: Ru1-P1 2.

Metallocages for Metal Anions: Highly Charged [Co@Ge9]5− and [Ru@Sn9]6− Clusters Featuring Spherically Encapsulated Co1− and Ru2− Anions

“…[36] TheS n À Sn distances (3.0512(8)-3.1409(6) )a re in anarrow range and on average considerably longer than those in empty [Sn 9 ] 4À (typically below 3 )b ut within the range of 2.86-3.64 observed in binary RuÀSn compounds.A ssuming an [Sn 9 ] 4À host polyhedron with an elongated trigonal-prismatic structure, [35] the endohedral Ru atom must also provide 10 electrons to the system, resulting in aformally twofold negatively charge for Ru. Compounds with Ru(ÀII) are rare,b ut have been found in isonitrile [37] and biphosphinine [38] complexes, whereas to the only known intermetalloid cluster, [Ru@Ge 12 ] 3À was attributed Ru(ÀI). [14c] An inspection of other [Sn 9 ]u nits reveals different structures for the empty,t he Co-filled, and the Ni-filled 22electron clusters,n amely C 4v for [Sn 9 ] 4À , [31] [Ni@Sn 9 ] 4À , [18a,b] and for the partially oxidized [Co 0.68 @Sn 9 ] 4À cluster with 21 SE, [15c] while [Cu@Sn 9 ] 3À shows D 3h symmetry.…”

Metallo‐Käfige für Metall‐Anionen: Hochgeladene [Co@Ge9]5−‐ und [Ru@Sn9]6−‐Cluster mit sphärisch eingelagerten Co−‐ und Ru2−‐ Anionen

“…Die Analyse der geometrischen Parameter (Tabelle 1) zeigt erneut Polyeder mit fast perfekter D 3h -Symmetrie mit neun nahezu gleichen Ru-Sn-Bindungslängen im engen Bereich 2.641-2.700 und in guter Übereinstimmung mit den entsprechenden Werten im binären System [36] ] 4À -Wirt-Polyeders mit einer elongierten trigonal prismatischen Struktur [35] muss das endohedrale Ru-Atom 10 Elektronen zum System beisteuern, wodurch eine formal zweifach negative Ladung fürR u resultiert. Ru(-II)-Verbindungen sind selten, wurden aber in Isonitril- [37] und Bisphosphinin-Komplexen [38] gefunden, wohingegen dem einzigen bisher bekannten Intermetalloid-Cluster [Ru@Ge 12 ] 3À Ru(-I) zugeschrieben wurde. [14c] Die Untersuchung anderer [Sn 9 ]-Cluster zeigt verschiedene Strukturen fürd ie leeren, die Co-gefüllten und die Nigefüllten 22-Elektronen-Cluster,n ämlich C 4v für[ Sn 9 ] 4À [31] und [Ni@Sn 9 ] 4À [18a,b] sowie fürd en partiell oxidierten [Co 0.68 @Sn 9 ] 4À -Cluster mit 21 SE, [15c] während [Cu@Sn 9 ] 3À D 3h -symmetrisch ist.…”