A Novel Diiminopyridine Ligand Containing Redox Active Co(III) Mixed Sandwich Complexes

Abstract

The synthesis of a diiminopyridine (DIMPY) ligand containing pendant mixed sandwich cobaltocene functionalities on the imine nitrogens was prepared and characterized (18). Its reactivity with 2 equiv of GeCl2·dioxane and SnCl2 in THF yields the respective Lewis base mediated autoionization products (18Ge and 18Sn). Analogous low-valent complexes utilizing an N,N'- differocenyl diiminopyridine support were also prepared (15Ge and 15Sn). All compounds were characterized by spectroscopic and X-ray crystallographic methods. Electrochemical studies were conducted for both 15Sn and the precursor of 18.

N-Coordinated Tin(II) Trifluoromethanesulfonates and Their Reactions with Transition Metal Carbonyls

“…Autoionization of GeX 2 (X = Cl, Br) induced by bi- or multidentate ligands was reported by Reid and Baines, respectively . Spontaneous dissociation of ECl 2 (E = Ge, Sn) was observed by Roesky et al reporting the syntheses and structures of [(DIMPY)­ECl] + cations (DIMPY = {2,6-[(CH 3 )­CN­(C 6 H 3 -2,6- i Pr 2 ) 2 ]­C 5 H 3 N}) that contain four-coordinated metal centers E ( A in Chart ), , and a similar result was observed by Ragogna, who employed a novel bis­(imino)­pyridine ligand containing redox-active cobaltocene and ferrocenyl functionalities ( B in Chart ) . Rowley et al also used the DIMPY ligand for the synthesis of [(DIMPY)­SnX]­[SnX 3 ] complexes (X = Cl, Br; C in Chart ) .…”

“…In contrast, a similar reaction of 3 provided compound [L 1 Sn II Cl][W(CO) 5 {Sn(OTf)Cl 2 }] ( 6), where one chloride anion of the SnCl 3 − moiety is substituted by a OTf − moiety at the [W(CO) 5 (SnCl 3 )] − anionic part, leaving the [L 1 SnCl] + cation noneffected. The reaction between 4 equiv of AgOTf and 3, however, provided the complex [L 1 SnOTf][OTf] (7), where the ligand L 1 and one triflate anion coordinates to the tin center. In contrast, the treatment of L 2 with Sn(OTf) 2 yielded neutral [L 2 Sn(OTf) 2 ] (8) with the ligand L 2 and both triflate anions being in the coordination sphere of the tin atom.…”

“…In addition, the reaction of complex 1 with 2 equiv of AgOTf again provided complex 5. In contrast, the reaction of 3 with 4 equiv of AgOTf yielded compound [L 1 SnOTf][OTf] (7). Interestingly, attempts at preparing 7 directly by treatment of ligand L 1 with Sn(OTf) 2 failed.…”

“…4 Spontaneous dissociation of ECl 2 (E = Ge, Sn) was observed by Roesky et al reporting the syntheses and structures of [(DIMPY)ECl] + cations (DIMPY = {2,6-[(CH 3 )CN(C 6 H 3 -2,6-i Pr 2 ) 2 ]C 5 H 3 N}) that contain fourcoordinated metal centers E (A in Chart 1), 5,6 and a similar result was observed by Ragogna, who employed a novel bis(imino)pyridine ligand containing redox-active cobaltocene and ferrocenyl functionalities (B in Chart 1). 7 Rowley et al also used the DIMPY ligand for the synthesis of [(DIMPY)SnX]-[SnX 3 ] complexes (X = Cl, Br; C in Chart 1). 8 A fascinating result was achieved by Fischer applying the DIMPY-type ligand for the stabilization of tin in oxidation state zero (D in Chart 1) and demonstrating the MeDIMPY ligand to give an Sn II enamine complex (E in Chart 1).…”

“…The analogous products containing the ligand L 2 were not isolated. Additionally, reactions of 1 and 3 with AgOTf gave the compounds [L 1 SnCl][OTf] (5), [L 1 SnCl][W(CO) 5 (SnCl 2 OTf)] ( 6), [L 1 SnOTf][OTf] (7), and [L 2 Sn(OTf) 2 ] (8), respectively.…”