Titanium σ-acetylides as building blocks for heterobimetallic transition metal complexes: synthesis and redox behaviour of π-conjugated organometallic systems

Abstract

A series of related Ti s-acetylides of the type {Ti}C CR ({Ti}= (h 5 -C 5 H 5 ) 2 Ti(CH 2 SiMe 3 ); 2: R=SiMe 3 ; 3: R= C 6 H 3 (CH 2 NMe 2 ) 2 -3,5; 4: R= C 6 H 2 I-4-(CH 2 NMe 2 ) 2 -3,5; 5: R=C 6 H 4 CN-4; 6: R= C 5 H 4 N-4; 7: R=Fc, Fc= (h 5 -C 5 H 4 )Fe(h 5 -C 5 H 5 ); 8: R=C 6 H 4 (C C{Ti})-4) have been prepared by reacting the corresponding lithium acetylides with {Ti}Cl (1). The X-ray crystal structure determination of {Ti}C CSiMe 3 ( 2) is reported. This compound exhibits a one-dimensional (1D) arrangement with respect to the Ti-C C unit. The reaction of 2 with [CuCl] n afforded 1 and [CuC CSiMe 3 ] n (10) and is proposed to occur via prior formation of the dimeric intermediate [(h 2 -{Ti}C CSiMe 3 ) 2 Cu 2 Cl 2 ]. The chemical oxidation of {Ti}C CFc, 7, with Ag[BF 4 ] yielded HC CFc and an undefined Ti species. Treatment of 5 or 6 with {Ru}N N{Ru} ({Ru} =mer,trans-[RuCl 2 (NN%N)]; NN%N= h 3 -C 5 H 3 N(CH 2 NMe 2 ) 2 -2,6) produced intensively coloured heterodinuclear compounds, such as [{Ti}C CC 5 H 4 N-4]{Ru} (16). In contrast, 5 and 6 react with cationic Pt compounds of the type [{Pt}•L][X] ({Pt} = [Pt(C 6 H 3 {CH 2 NMe 2 } 2 -2,6] +; L= H 2 O, MeCN; X =BF 4 , OTf) to give product mixtures rather than defined compounds. Electrochemical studies on some of the bimetallic compounds show that the Ti(III)/Ti(IV) redox potential appears to be reversible and is shifted to a more negative value upon substitution of the Cl ligand in 1 by C CR (compounds 2-8). Whereas the nature of R in {Ti}C CR has an influence on the Ti(III)/Ti(IV) redox potential, the attachment of a second metal onto the p-conjugated system has only negligible effect on the electrochemical properties of the Ti centre.

Heterotrimetallic and heterotetrametallic transition metal complexes

“…This potential is similar to that found in {Ti}(C"C-C 5 H 4 N-[Ru]) ({Ti} = (g 5 -C 5 H 5 ) 2 Ti(CH 2 SiMe 3 )). In comparison with [Ru]-NC 5 H 5 , the ruthenium oxidation potential of 12 is shifted to a more negative value indicating that the oxidation is facilitated by the presence of a platinum building block in para-position [21]. Measuring the cyclic voltammograms upto 1.6 V results in the appearance of an additional irreversible oxidation wave at E p,ox = 1.27 V (Fig.…”

Alkyloxy- and aryloxy-titanocenes: Synthesis, solid-state structure and cyclic voltammetric studies

“…Exchange of one methyl group by a [Ti]Cl unit (9, n = 1) shifts the oxidation potential by 0.37 V to more negative values. A second replacement (14, n = 2) leads to a further shift of 0.25 V. The magnitude of the shift is very notable since, for example, in (g 5 -C 5 H 5 ) 2 Ti(CH 2 SiMe 3 )(C"CFc) the ferrocene oxidation is only facilitated by 0.080 V as compared to HC"CFc [29]. Therefore, it can be concluded that in 9, 14 and 15 an effective resonance stabilization of the oxidized species (radical cation) takes place.…”

“…13 C{ 1 H} NMR (CDCl 3 ): [d] À0.3 (SiMe 3 ), 111.5 (C 2 H/ C 6 H 4 ), 114.0 (C 6 H/C 6 H 4 ), 115.0 (CH/C 5 H 4 ), 119.1 (CH/C 5 H 4 ), 123.8 (C 4 H/C 6 H 4 ), 127.2 (CH/C 5 H 4 ), 128.9 (CH/C 5 H 4 ), 129.4 ( i C/C 5 H 4 ), 130.4 (C 5 H/C 6 H 4 ), 149.0 ( i C 3 H/C 6 H 4 ), 170.2 (C-OTi). 29 [Ti](OC 6 H 4 -4-NO 2 ) 2 (13)…”

Titanium Triamidotriamine Compounds: Syntheses, Structures and Redox Properties

“…Triazacycloundecane derivatives are, in general, less stable than the triazacyclononane-based complexes and this characteristic prevents their study by cyclic voltammetry. The stability of the cations is higher than that of the reduced metal complexes and thus [Ti{N 3 [9] [16][17][18] On the other hand, the value of -1.58 mV measured for E 1/2 red of 7 reflects the additional stability of the LUMO when C 6 H 5 is replaced by o-C 6 H 4 F. The similarity between the reduction potential of 7 and that of [Ti{O 3 [9]-N 3 }PF 6 (H 3 O 3 [9]N 3 = 1,4,7-tris(5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane; E 1/2 red = -1.52 mV) shows that the donor ability of the amide moieties in 7 is comparable to that of the alkoxide fragments in [Ti{O 3 [9]N 3 }]PF 6 . [17] The voltammograms of 7 and 9 display addition redox peaks at -0.22 V and -0.20 V, respectively, that are due to the I -counterion.…”