Synthesis and reactivity of titanium/cobalt complexes with Ti-O-C-Co bridges

Abstract

Reactions between titanium metallocene dicarbonyls and dicobalt octacarbonyl were investigated and found to give a variety of Ti/Co complexes depending on the reaction conditions. Reaction between CpzTi(CO)z and C O~( C O )~ in nondonor solvents led to the formation of the known CpzTi[OCCo3(CO)9]z via a novel redox/cluster-building process. However, reaction between CP,T~(CO)~ and CO,(CO)~ in tetrahydrofuran led to the formation of the ionic compound [CP~T~(THF)~] [Co(CO),]. A mechanism in which isocarbonyl bridge formation is required to build the cluster compounds is proposed. Reaction between CP*~T~(CO)~ (Cp* = pentamethylcyclopentadienyl) and CO~(CO)~ yields the Ti(1V) isocarbonyl-bridged complex Cp*zTi[OCCo(CO),]z from toluene but gives the paramagnetic Ti(II1) dimer [Cp*zTiOCCo(CO)p]2 from hexane solution. Reactions of the above Ti/Co complexes with triphenylphosphine induce inner-sphere electron transfer from Co to Ti to take place via the isocarbonyl bridge. IntroductionThe study of reactions combining transition-metal group IV complexes (as well as lanthanide compounds) with metal carbonyl compounds later in the transition series has yielded a wealth of complexes with unusual structures.z In many cases, the dominant feature in the structures obtained is the presence of M-O-C-M' bridges, a bonding mode to which we will refer as isocarbonyl bridges. In previous reports we discussed the syntheses, molecular structures, and reaction chemistry of complexes containing both titanium and molybdenum that are held together by these isocarbonyl bridges2gJ Our synthetic route to these Ti/Mo compounds exemplifies the underlying concept of our synthetic strategy for obtaining early/late transition metal combinations: the reaction of a low-valent group IV metal complex with a reactive later transition-metal dimer.We turned our attention to applying this strategy to the synthesis of early/late metal compounds utilizing cobalt carbonyl as the later transition-metal complex. This approach led both to the synthesis of some known compounds through novel redox routes and to the synthesis of some new and unusual Ti/Co complexes. This paper discusses the results of our synthetic program to make Ti/Co combination materials and some reactions that show the importance of electron transfer mediated by the isocarbonyl bridge in the chemistry of these Ti/Co complexes. ResultsWe found that the general concept for forming early/late metal complexes that we applied in our Ti/Mo work, Le. the reaction of a low-valent group IV metal complex with a reactive metal dimer, served us well in the case of the reaction between CpzTi(CO)z and C O~( C O )~. However, we found the chemistry to be quite complex and highly dependent on such factors as the nature of the solvent and the substitution on the cyclopentadienyl rings on the titanium. Each of these effects will be discussed in turn in the following subsections.

Formation, Structure, and Dynamic Behavior of a Novel Dinuclear Cationic μ-2,4-Hexadiyne Bis(zirconocene) Complex

“…c The blue bis(cyclopentadienyl)bis(tetrahydrofuran)titanium(III) tetraphenylborate salt was isolated and identified by an X-ray crystal structure analysis. The molecular structure of the Cp 2 Ti(THF) 2 + cation in the crystal structure of 7 is analogous to the structures recently observed for several closely related examples ([Cp 2 Ti(THF)(acetonitrile) + ]BPh 4 - ,9a [Cp 2 Ti(THF) 2 + ]Co(CO) 4 - ,9b and [Cp 2 Ti(pyridine) 2 + ]BPh 4 - 9c ). In 7 , the (THF−oxygen)−Ti−(THF−oxygen) angle is 77.49(7)°; the corresponding Ti−O distances are 2.208(2) and 2.239(2) Å (further details about the structure of 7 are provided with the Supporting Information).…”

“…In contrast, the (σ-propynyl)(tetrahydrofuran)TiCp 2 + cation is decomposed in ca. 3 days at ambient temperature to yield the known paramagnetic titanium(III) complex [Cp 2 Ti(THF) 2 + ]BPh 4 - ( 7 ) 9a…”

Novel Titanium−Cobalt Complexes Formed by Reductive Cleavage of a Co−Co Bond in Co2(CO)8 by Titanocene tert-Butoxides: Synthesis, Characterization, and Mechanistic Aspects for Metal−Metal Bond Recombination

“…As described above, the Ti atom in all of the reported Ti−Co 3 complexes is linked to the Co 3 moiety by an isocarbonyl bridge. In contrast, it is known that there are two types of Ti−Co heterobimetallic complexes: one is the type that has a Ti−OC−Co isocarbonyl bridge, ,,, whereas the other is the type that bears a Ti−Co direct bond . As shown in Figure , the molecular structure of 5 revealed that 5 is a heterobimetallic complex whose two metals are linked by an isocarbonyl bridge, Ti−OC−Co.…”

Carbonylation of Heterocycles by Homogeneous Catalysts.

“…A survey conducted of the Cambridge Structural Database for such compounds revealed [Cp 2 Ti(THF) 2 ] + [Co(CO) 4 ] 2 , 7, an easily synthesized complex. 56 This compound was active for epoxide carbonylation, though less robust and efficient than 1. However, 7 proved to be a very active catalyst for aziridine carbonylation, producing several b-lactams in good or excellent yield.…”

“…The well-defined nature of catalyst 1 has permitted us to design a number of related catalysts for epoxide-expansion carbonylation (Scheme 13). [49][50][51][52][53][54][55] We have also found that the 56 7, is an active catalyst for this reaction, though it finds greater utility in aziridine carbonylation (see section 6.2). 57 Each of these catalysts features a metal cation to which two THF ligands are bound in the solid state, substantiating its Lewis acidity.…”