Consuelo Moreno

Synthesis and electrochemical study of cobalt carbonyl complexes of trimethylsilyl-substituted 1,3,5-triethynylbenzene

Treatment of 1,3,5-tris(trimethylsilylethynyl)benzene or 1,3,5-triethynylbenzene with Co 2 (CO) 8 or Co 2 (CO) 6 (dppm) produced the formation of substituted ethynylcobalt complexes with one, two or three Co 2 (CO) 6 or Co 2 (CO) 4 (dppm) units, [{X 3 (Co 2 (CO) 6 )C 2 } n (XCC) m (1,3,5-C 6 H 3 )] (X=H or SiMe 3 ) ( n =1, 2 or 3; m =3− n ) and [{SiMe 3 (Co 2 (CO) 4 dppm)C 2 } n (SiMe 3 CC) m (1,3,5-C 6 H 3 )] ( n =1 or 2; m =3− n ), in a high yield. Desilylation of the non-metallated alkynes in [{SiMe 3 (Co 2 (CO) 4 dppm)C 2 }(SiMe 3 CC) 2 (1,3,5-C 6 H 3 )] occurred on treatment with KOH. Electrochemical results provide evidence for communication between the C 2 Co 2 centres. Crystals of [{SiMe 3 (Co 2 (CO) 4 dppm)C 2 } 2 (SiMe 3 CC)(1,3,5-C 6 H 3 )] suitable for single-crystal X-ray diffraction were grown and the molecular structure of this compound is discussed.

Alkynyl cobalt complexes. An electrochemical study

Abstract The preparation and characterisation of the complexes Co2(CO)5(PMe3)(μ-η2-Me3SiC2CCSiMe3) (2) and Co2(CO)4(PMe3)2(μ-η2-Me3SiC2CCSiMe3) (3) are described. A comparative electrochemical study of the complexes Co2(CO)6−nLn(μ-η2-Me3SiC2CCSiMe3) (n=0 (1); n=1, L=PMe3 (2); n=2, L=PMe3 (3), PPh2Me (4), dppa (5), dppm (6)) is presented by means of the cyclic and square-wave voltammetry techniques. Substitution of CO by phosphine ligands transforms the Co2C2 redox centre from a readily reducible to an easily oxidisable centre and contributes to the stabilisation of the Co–Co bond increasing the lifetime of the radical cations and anions.

SYNTHESIS AND CHARACTERIZATION OF NEW TRANSITION METAL DIYNYL COMPLEXES

The reaction of (η 5 -C 5 H 5 )Mo(CO)(dppe)Cl with LiCCCCSiMe 3 yielded (η 5 -C 5 H 5 )(CO)(dppe)MoCCCCSiMe 3 ( 1b ) and, as a by-product (η 5 -C 5 H 5 )Mo(CO)(dppe)Br ( 1a ). Treatment of 1b with 0.2 equivalents of tetrabutylammonium fluoride or (η 5 -C 5 H 5 )Mo(CO)(dppe)Cl with HCCCCH gave the terminal butadiyne complex (η 5 -C 5 H 5 )(CO)(dppe)MoCCCCH ( 2 ). Complex 2 was deprotonated with sec -BuLi or lithium diisopropylamide, and the resulting anion (η 5 -C 5 H 5 )(CO)(dppe)MoCCCCLi ( 3 ) was trapped with Me 3 SiCl to regenerate 1b . The synthesis of Co 2 (CO) 4 L 2 (μ-η 2 -Me 3 SiC 2 CCSiMe 3 ) (L 2 =dppa 4 , 2PPh 2 Me 5 ) compounds can be achieved by two methods: from Co 2 (CO) 6 (μ-dppa) by reaction with Me 3 SiCCCCSiMe 3 in 1:1 ratio to yield 4 , or from Co 2 (CO) 6 (μ-η 2 -Me 3 SiC 2 CCSiMe 3 ) by reaction with dppa (1:1 ratio) and PPh 2 Me (1:2 ratio) to yield 4 and 5 , respectively. When the Co 2 (CO) 4 (μ-dppa)(μ-η 2 -Me 3 SiC 2 CCSiMe 3 ) complex was treated with more Co 2 (CO) 6 (μ-dppa) the green di-substituted complex [Co 2 (CO) 4 (μ-dppa)] 2 (μ-η 2 :μ-η 2 -Me 3 SiC 2 C 2 SiMe 3 ) ( 6 ) was obtained. Desilylation of 4 with Bu 4 NF gave Co 2 (CO) 4 (μ-dppa)(μ-η 2 -Me 3 SiC 2 CCH) ( 7 ). All compounds synthesized have been characterized by analytical and spectroscopic data (IR, 1 H-, 31 P-, 13 C-NMR, MS). In addition, compounds 1a and 4 were characterized by X-ray structure analysis.

Reactions of Co2(CO)8 with potentially polydentate phosphines

Abstract Co2(CO)8 reacts with potentially polydentate phosphines such as Ph2Ppy (2-(diphenylphosphino)pyridine), t-dppv (trans-1,2-vinylenebis(diphenylphosphine)), dppa (bis(diphenylphosphino)amine) and dpmp (bis((diphenylphosphino)methyl)phenylphosphine) to give Co2(CO)6L2 (L=Ph2Ppy and t-dppv), Co2(CO)6(dppa) and Co2(CO)5(dpmp) where the ligands behave as mono-, di- and tridentate, respectively, via the ionic intermediates [Co2(CO)3L2][Co(CO)4] (L=Ph2Ppy and t-dppv) and [Co(CO)3 P P ][Co(CO)4] ( P P =dppa and dpmp). All the compounds have been characterized by elemental analysis, IR, electronic, 1H and 31P NMR spectroscopy.

Steric limitations in associative substitution reactions of Os3(CO)9(μ-C4Ph4)

Abstract Reactions of the cluster Os3(CO)9(μ-C4Ph4) (1) with a large number of smaller P-donor nucleophiles (Tolman cone angle θ ≤ 143°) proceed rapidly in heptane at room temperature via associative adduct formation to form the monosubstituted products. However, reactions with several larger P-donor nucleophiles (θ ≥ 145°) in heptane at room temperature yield, in a single observable bimolecular step, a mixture of mononuclear and dinuclear products and it is therefore not possible to synthesize the monosubstituted clusters directly with these larger ligands. Crystallographic structures of Os3(CO)8(etpb)(μ-C4Ph4)·(CH3OH) (2etpb) (etpb = P(OCH2)3CEt) and Os3(CO)8-(P(OPh)3)(μ-C4Ph4)·(C6H14) (2P(OPh)3) have been determined and show that the substituent has displaced a CO ligand from the Os(CO)4 moiety in 1.

Electrochemical study of methylfulvalene and methylcyclopentadiene molybdenum complexes

Abstract The product of the synthesis of ( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 ( 1 ) is reported as a mixture of six stereoisomers, the ratio of which has been unambigously assigned using homonuclear two dimensional correlation spectroscopy (COSY and NOESY). The reaction of Li 2 [( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 ] ( 2 ) with IMe yields ( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 Me 2 ( 3 ) and that of 1 with I 2 yields ( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 I 2 ( 4 ). The electrochemical behaviour of 1 , 3 , and 4 is reported and compared with analogous complexes where other substituents are present on the fulvalene rings. Electronic communication through the fulvalene ligand seems to take place in 4 . The related compounds [( η 5 -C 5 H 4 R)Mo(CO) 3 ] 2 (R=Me ( 5 ), H ( 9 )), ( η 5 -C 5 H 4 R)Mo(CO) 3 Me (R=Me ( 7 ), H ( 10 )) and ( η 5 -C 5 H 4 R)Mo(CO) 3 I (R=Me ( 8 ), H ( 11 )) have been synthesized in order to compare their electrochemical behaviour with the fulvalene analogous.

Comparative reactivity study of cyclopentadienyl and fulvalene molybdenum complexes

The reactions of cis-1,1%-[h 5 :h 5 -(C5H3CO2Me)2]Mo2(CO)6 (1), in the presence of 1 equiv. of Me3NO, and [(h 5 C5H4CO2Me)Mo(CO)3]2 (2) with dppe produce CO labilization and formation of the dinuclear zwitterions trans-1,1%-[h 5 :h 5 (C5H3CO2Me)2]Mo2(CO)5(dppe) (3) and disproportionation species [(h 5 -C5H4CO2Me)Mo(CO)2(dppe)] [(h 5 -C5H4CO2Me)Mo(CO)3] (4), respectively. Using the same method, the reactions of trans-1,1%-[h 5 :h 5 -(C5H3CO2Me)2]Mo2(CO)6I2 and (h 5 C5H4CO2Me)Mo(CO)3I with PPh3 in the presence of 1 and 2 equiv. of Me3NO yield trans-1,1%-[h 5 :h 5 -(C5H3CO2Me)2]Mo2(CO)4(PPh3)2I2 (5) and (h 5 -C5H4CO2Me)Mo(CO)2(PPh3)I (6). The reactions of the several anionic carbonyl species {trans1,1%-[h 5 :h 5 -(C5H3CO2Me)2]Mo2(CO)6} 2 ,[ ( h 5 :h 5 -C10H8)W2(CO)6] 2 and [(h 5 -C5H4CO2Me)Mo(CO)3] with S2Ph2 give rise to the thiolate‐fulvalene complexes cis-1,1%-[h 5 :h 5 -(C5H3CO2Me)2]Mo2(CO)4(m-SPh)2 (7) and (h 5 :h 5 -C10H8)W2(CO)6(SPh)2 (8) and the thiolate-bridged dimer [(h 5 -C5H4CO2Me)Mo(CO)(m-SPh)]2 (9). Treatment of 6 with 1 equiv. of HCCCCH and with (h 5 -C5H5)Mo(CO)(dppe)(CCCCH), in the presence of CuI at room temperature, afford the cyclopentadiene complexes (h 5 -C5H4CO2Me)Mo(CO)2(PPh3)(CCCCH) (10 )a nd ( h 5 -C5H4CO2Me)(PPh3)(CO)2Mo(CCCC)Mo(CO)(dppe)(h 5 -C5H5) (11), respectively. The reaction of (h 5 -C5H5)Mo(CO)(dppe)(CCCCH) with Co2(CO)8 yields [Co2{m-HC2CC[Mo(CO)(dppe)(h 5 -C5H5)]}(CO)6 ]( 12). All the new compounds have been characterized by analytical and spectroscopic methods.

[Co4(CO)12] derivatives with bis(diphenylphosphino) amine, an electrochemical study

Abstract [CO 4 (CO) 12 ] ( A ) reacts with bis(diphenylphosphino)amine (dppa) to give [Co 4 (CO) 10 (dppa)] ( B ) or [Co 4 (CO) 8 (dppa) 2 ] ( C ) when the reactant ratios are 1:1 or 1:2, respectively. The complexes have been characterized by elemental analysis, IR, 1 H and 31 P NMR spectroscopy. The electrochemical behaviour of the three compounds has been studied. The reduction voltammetric waves and the first oxidation of C are reversible, although other waves were also observed which were attributed to the fragmentation induced by electron transfer. Using the electrochemical and UV-visible data, it was possible to construct MO diagrams and to locate the HOMO, LUMO and other MOs of the metal core.

Stabilization of 17-electron metal-centered species. Electrochemical study of [WX(CO)3(η5-C5H5)] (X=Cl, Br, I) and [WI(CO)2(PCy3)(η5-C5H5)]

The electrochemical study of [WX(CO)3(η5-C5H5)] (X=Cl, Br, I) (1–3) is reported. The reductions follow ECE mechanisms, yielding the anion [W(CO)3(η5-C5H5)]− (7−). The stability of 1–3 towards reduction increases with the increasing electronegativity and decreasing size of the halide. 7− reoxidizes to the unstable 17-electron radical [W(CO)3(η5-C5H5)] (7), which readily dimerizes. The oxidations of 1–3 follow EC mechanisms, leading to the cations [WX(CO)3(η5-C5H5)]+, which are very unstable and readily decompose. [WI(CO)2(PCy3)(η5-C5H5)] has been prepared and characterized as a mixture of cis (4) and trans (5) isomers (ratio cis:trans 95:5). The electrochemical reduction of the cis isomer (4) is also an ECE process, but takes place at a potential significantly more negative than 3. An anion [W(CO)2(PCy3)(η5-C5H5)]− (8−) is formed which reoxidizes to 8. This new 17-electron radical is considerably more stable than 7 due to the presence of the bulky PCy3 ligand. A similar effect is observed in the oxidation of 4, where the 17-electron product 4+ is significantly more stable than the analogue 3+.

Carbonyl substitution reactions of cyclopentadienyldicarbonyl cobalt(I) and acetylcyclopentadienyldicarbonyl cobalt(I) with bis(1,3-dimethylimidazolin-2-ylidene). A kinetic and mechanistic study

Abstract The reaction of (η5-Cp′)Co(CO)2 (Cp′ = C5H5, C5H4COMe) with bis(1,3-di- methylimidazolin-2-ylidene) gives the monosubstituted products (η5-Cp′)Co(CO) [ C(NMe)CH 2 CH 2 (N Me)]. The reaction proceeds by first order in metal complex and first order in olefin. The rate of replacement of CO by the carbene fragment for (η5- C5H4COMe)Co(CO)2 in toluene at 95†C is 15 times faster than for the reaction of (η5- C5H5)Co(CO)2. The reasons for this difference are discussed in mechanistic terms.