Synthesis and reactivity of heterometallic platinum-ruthenium and iron-osmium nitrido complexes

Abstract

The nitrido group is a versatile bridging ligand that can bind to two metal ions either symmetrically or unsymmetrically. While dinuclear nitrido complexes containing earlier and mid transition metals are well known, there are few heterometallic μ-nitrido complexes with late transition metals such as platinum. This thesis reports on the synthesis and reactivity of heterobimetallic platinum-ruthenium and iron-osmium nitrido complexes. In Chapter 2, the synthesis and structure of heterodinuclear platinum-ruthenium complexes are described. Treatment of the previously reported Pt(II) cyclometalated complex [Pt(C^N^C)(dmso)] (1) (H₂(C^N^C) = 2,6-di(4-tert-butylphenyl)pyridine; dmso = dimethylsulfoxide) with [L_OEtM(N)Cl₂] (M = Ru, Os; L_OEt^- = [Co(η⁵-C₅H₅){P(O)(OEt)₂}₃]^-) afforded air-stable heterometallic Pt(II)/M(VI) nitrido complexes [L_OEtMCl₂(μ-N)Pt(C^N^C)] (M = Ru, Os) (M = Ru (2-1), Os (2-2) that have been characterized by X-ray diffraction. The Ru-N and Pt-N(nitrido) distances in 2-1 [1.679(5) and 1.815(5) Å, respectively] are indicative of the Ru=N=Pt bonding description. The oxidation of 2-1 with PhICl₂ yielded the Pt(IV)/Ru(VI) complex [L_OEtRuCl₂(μ-N)PtCl₂(C^N^C)] (2-3). The Pt-N distance in the Pt(IV) complex 2-3 [1.893(3) Å] is significantly longer than that in the Pt(II) analogue 2-1 [1.815(5) Å] because the π bonding between Pt and the Ru nitride is weakened when the oxidation state of Pt increases from +2 to +4. Treatment of 1 with [ⁿBu₄N][Ru(N)Cl₄] in tetrahydrofuran (THF) afforded [ⁿBu₄N][(THF)Cl₄Ru(μ-N)Pt(C^N^C)] (2-4). Chloride substitution of 2-4 with K[N(Ph₂PS)₂] afforded [{N(Ph₂PS)₂}₂Ru(μ-N)PtCl₂(C^N^C)]Cl (2-5) that has been characterized by X-ray diffraction. The short Pt-N bond distance in 2-5 [1.808(2) Å] is consistent with a Pt=N double bond. Chapter 3 describes the synthesis and structure of heterometallic iron(IV) nitrido complexes. Treatment of [Fe(Pc)] (Pc^2- = phthalocyanine dianion) with [L_OEtOs(N)Cl₂] afforded a novel trinuclear μ-nitrido complex [(Pc)Fe{L_OEtOsCl₂(μ-N)}₂] (3-1) that has been characterized by X-ray diffraction. The Os-N and Fe-N(nitride) distances in 3-1 are 1.677(6) and 1.841(6) Å, respectively, and the Os-N-Fe angles are 170.0(4)^o. The structural data of 3-1 is consistent with the Os(V)-Fe(IV)-Os(V) formulation. The oxidation of 3-1 with [(4-BrC₆H₄)₃N](SbCl₆) in CH₂Cl₂ resulted in the appearance of absorption bands at 603 and 665 nm in the UV/visible spectrum that are diagnostic of Pc cation radical. As such, the 1-electron oxidation product of 3-1 is formulated as a Os(V)-Fe(IV) Pc cation radical complex, [(Pc^.+)Fe{L_OEtOsCl₂(μ-N)}₂]. Treatment of [Fe(bpb)] (H₂bpb = 1,2-bis(pyridine-2-carboxamido)benzene), which was prepared in-situ by Zn reduction of (ⁿBu₄N)[Fe(bpb)Cl₂], with [L_OEtRu(N)Cl₂] afforded the Ru(IV)-Fe(IV) nitrido complex [(L_OEtCl₂Ru(μ-N)Fe(bpb)] (3-2) that was characterized by NMR spectroscopy. Similarly, [(L_OEtCl₂Ru(μ-N)Fe(tmtaa)] (H₂tmtaa = 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecane) was prepared by the reaction of [Fe(tmtaa)] with [L_OEtRu(N)Cl₂] and characterized by NMR spectroscopy.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology