Synthesis and reactivity of the paramagnetic nitrosyl complexes [M(NO)(NCMe)5]2+(M = Cr or Mo), and the crystal structures of [Cr(NO)(S2CNEt2)3] and [CrF(NO)(dppe)2]

Abstract

Excess of [NO]Y (Y = BF₄ or PF₆) and [M(CO)₆] in acetonitrile afford paramagnetic [M(NO)(NCMe)₅]Y₂(1; M = Cr or Mo) which reacts with NO gas (M = Mo) to give diamagnetic cis-[Mo(NO)₂(NCMe)₄]Y₂. At room temperature (1; M = Cr) and [S₂CNR₂]^– yield [Cr(NO)(S₂CNR₂)₃](2; R = Me or Et) which affords cis-[Cr(NO)₂(S₂CNR₂)₂] and [Cr(S₂CNR₂)₃] in refluxing toluene; only cis-[Cr(NO)₂{S₂C₂(CN)₂}₂]^2– is isolable from the reaction between (1; M = Cr) and Na₂[S₂C₂(CN)₂]. A crystal-structure determination of (2; R = Et) has revealed the geometry about chromium to be pentagonal bipyramidal with the nitrosyl ligand in an axial position; crystals are triclinic, space group P, with Z= 2, in a unit cell of dimensions a= 9.525(3), b= 9.903(5), c= 14.649(7)Å, α= 103.8(4), β= 74.5(3), and γ= 107.4(3)°. The structure has been solved from diffractometer data by the heavy-atom method, and refined to R = 0.040 for 3 033 observed reflections.

With 1,2-bis(diphenylphosphino)ethane (dppe) in acetonitrile (1; M = Cr or Mo) affords [M(NO)(NCMe)(dppe)₂]Y₂(3; M = Cr) and [M(NO)(NCMe)(dppe)₂]Y (4; M = Mo) which is oxidised to (3; M = Mo) by [N₂C₆H₄F-p]Y. Dppe and (1; M = Cr) also give [CrX(NO)(dppe)₂]Y (5; X = F) which is reduced, as is (3; M = Cr), by Na[BH₄] in tetrahydrofuran to [CrX(NO)(dppe)₂](6; X = F). The crystal structure of (6; X = F) has verified the trans disposition of the NO and F ligands; crystals are monoclinic, space group P2₁/n, with Z= 2, in a unit cell of dimensions a= 11.080(6), b= 16.352(6), c= 13.129(7)Å, and β= 109.17(4)°. The structure has been solved from diffractometer data by the heavy-atom method, and refined to R= 0.047 for 2 633 observed reflections.

Complexes (3) and (4) react with chloride ion to give [MX(NO)(dppe)₂]Y (5; M = Cr or Mo, X = Cl) and [MX(NO)(dppe)₂](6; M = Mo, X = Cl) respectively, which are interconvertible by [N₂C₆H₄F-p]Y oxidation [(6) to (5)] or Na[BH₄] reduction [(5) to (6)]. The redox properties of complexes (1)–(6) have also been studied, by cyclic voltammetry, and the retention during electron transfer of the mutually trans disposition of the dppe ligands of (3)–(6) verified by ³¹P n.m.r. and e.s.r. spectroscopy.