Alkynyl Ti–M complexes with M = Cd and Hg: Synthesis, characterization, and reaction chemistry

The synthesis and properties of heterobimetallic Ti–Cd complexes of type {[Ti](μ-η1:η2–CCR)2}CdX2 ([Ti] = Ti(η5–C5H4SiMe3)2; R = SiMe3: 3a, X = Cl; 3b, X = Br; 3c, X = I; R = Fc: 3d, X = Br; Fc = Fe(η5–C5H4)(η5–C5H5) is reported. These compounds were accessible by treatment of [Ti](CCR)2 (1a, R = SiMe3; 1b, R = Fc) with the cadmium salts CdX2 (2a, X = Cl; 2b, X = Br; 2c, X = I) in a 1:1 M ratio in diethyl ether. Dissolving, for example, 3b in tetrahydrofuran afforded coordination polymer [Cd(μ-Br)2(thf)2]n (4) along with the tweezer molecule 1a. Treatment of 3b with two equiv of LiCCFc (5) gave {[Ti](μ-η1:η2–CCSiMe3)2}Cd(CCFc)2 (6) which eliminated at ambient temperature the all-carbon buta-1,3-diyne FcCC–CCFc (7) producing 1a and elemental Cd. The same reaction behavior was observed, when 2b was reacted with 5. The thus obtained bis(alkynyl) cadmium complex Cd(CCFc)2 (8) is redox-active at low temperature producing 7 and Cd(0). When mercury halides HgX2 (9a, X = Cl; 9b, X = Br) are used, then the titanocene dihalides [Ti]X2 (10a, X = Cl; 10b, X = Br) together with Me3SiCC–CCSiMe3 (11) and Hg(0) were formed. Nevertheless, mercury acetylides were available by treatment of Hg(OAc)2 (12) with HCCFc (13) in a 1:2 M ratio. Thus obtained Hg(CCFc)2 (14) gave with [CuBr] (15) coordination polymer [{Hg(η2-CCFc)2}(Cu2(μ-Br)2]n (16), while with [AgPF6] oxidation of the ferrocenyl moieties took place affording dicationic [Hg(CCFc)2]2+ (18).The structures of 3b and 4 in the solid state are reported. Compound 3b shows the typical characteristics for heterobimetallic organometallic π-tweezer complexes with cadmium in a tetrahedral environment, while 4 corresponds to a one-dimensional coordination polymer in which the Cd(II) ions are linked in a edge-sharing fashion by bromide bridges in the pseudo-equatorial plane. The appropriate tetrahydrofuran molecules are completing the pseudo-octahedral coordination sphere at cadmium.The cyclic voltammogram of 14 is reported showing a single reversible redox event at E0 = 0.108 V with ΔEp = 76 mV indicating that there is no communication between the Fc termini along the mercury acetylide unit.

The synthesis, properties and reaction behavior of heterobimetallic complexes of type {[Ti](μ-η1:η2–CCR)2}CdX2 ([Ti] = Ti(η5–C5H4SiMe3)2; R = SiMe3, Fc; X = Cl, Br, I; Fc = Fe(η5–C5H4)(η5–C5H5) and M(CCFc)2 (M = Cd, Hg), and coordination polymers [{Hg(η2–CCFc)2}(Cu2(μ-Br)2]n and [Cd(μ-X)2(thf)2]n, respectively, is reported. The structure of two samples in the solid state is envisaged.Figure optionsDownload as PowerPoint slideHighlights
► Organometallic p-tweezer chemistry for stabilizing low-valent transition metal species.
► Stabilization of cadmium and mercury ferrocenylacetylides by the chelating effect of a organometallic 1,4 diyne.
► Formation of heterobi- and heterotrimetallic early-late transition metal complexes.
► Formation of a 1D coordination polymer based on cadmium dibromide and tetrahydrofuran.