Palladium catalyzed Suzuki coupling reactions using cobalt-containing bulky phosphine ligands

Three bulky mono-dentate alkyne-bridged dicobalt-phosphine complexes [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-PhCCPPh₂) 4a, [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-Me₃CCCPPh₂) 5a and [(μ-PPh₂CH₂PPh₂)Co₂(CO)₄](μ,η-Me₃SiCCPPh₂) 6a were prepared from the reactions of the bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex Co₂(CO)₆(μ-Ph₂PCH₂PPh₂) with PhCCPPh₂1, Me₃CCCPPh₂2, and Me₃SiCCPPh₂3, respectively. These three metal-containing compounds 4a, 5a and 6a were employed as ligands, replacing conventional organic phosphines, in the Suzuki cross-coupling reactions and have been proved to be effective, authentic mono-dentate phosphine ligands.     

Reactions of a phosphido-bridged unsymmetrical diiron complex (η-C5Me5)Fe2(CO)4(μ-CO)(μ-PPh2) with various alkynes

A phosphido-bridged unsymmetrical diiron complex (η⁵-C₅Me₅)Fe₂(CO)₄(μ-CO)(μ-PPh₂) (1) was synthesized by a new convenient method; photo-dissociation of a CO ligand from (η⁵-C₅Me₅)Fe₂(CO)₆(μ-PPh₂) (2) that was prepared by the reaction of Li[Fe(CO)₄PPh₂] with (η⁵-C₅Me₅)Fe(CO)₂I. The reactivity of 1 toward various alkynes was studied. The reaction of 1 with ^tBuCCH gave a 1:1 mixture of two isomeric complexes (η⁵-C₅Me₅)Fe₂(CO)₃(μ-PPh₂)[μ-CHC(^tBu)C(O)] (3) containing a ketoalkenyl ligand. The reactions of 1 with other terminal alkynes RCCH (R=H, CO₂Me, Ph) afforded complexes incorporating one or two molecules of alkynes and a carbonyl group. The principal products were dinuclear complexes bridged by a new phosphinoketoalkenyl ligand, (η⁵-C₅Me₅)Fe₂(CO)₃(μ-CO)[μ-CR¹CR²C(O)PPh₂] (4a: R¹=H, R²=H; 4b: R¹=CO₂Me, R²=H; 4c: R¹=H, R²=Ph). In the cases of alkynes RCCH (R=H, CO₂Me), dinuclear complexes having a new ligand composed of two molecules of alkynes, a carbonyl group, and a phosphido group; i.e. (η⁵-C₅Me₅)Fe₂(CO)₃[μ-CRCHCHCRC(O)PPh₂] (5a: R=H; 5b: R=CO₂Me), were also obtained. In all cases, mononuclear complexes, (η⁵-C₅Me₅)Fe(CO)[CR¹CR²C(O)PPh₂] (6a: R¹=H, R²=H; 6b: R¹=H, R²=CO₂Me; 6c: R¹=H, R²=Ph) were isolated in low yields. The structures of 1, 4c, 5b, and 6a were confirmed by X-ray crystallography. The detailed structures of the products and plausible reaction mechanisms are discussed.     

Discovering the chemical reactivity of the molecular oxonitride [{Ti(η-C5Me5)(μ-O)}3(μ3-N)]

The ability of the oxonitride [{Ti(η⁵-C₅Me₅)(μ-O)}₃(μ₃-N)] (1) to act as an organometallic ligand has been studied from both theoretical and experimental points of view. DFT calculations have allowed understanding the electronic structure of 1, and rationalizing its chemical behavior by comparison with the electronic structures of isoelectronic species [{Ti(η⁵-C₅Me₅)(μ-O)}₃(μ₃-CH)] and [{Ti(η⁵-C₅Me₅)(μ-NH)}₃(μ₃-N)]. Reactions of 1 with different inorganic molecules such as [Mo(CO)₃(1,3,5-Me₃C₆H₃)] or AlEt₃ have confirmed the possibility of 1 to act as a tridentate or monodentate ligand to give the [{(CO)₃Mo}(μ₃-O)₃{Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (2) and [{Et₃Al}(μ₃-O){(μ-O)₂Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (3) complexes, respectively. Surprisingly, reactions of 1 with [M(CO)₆] (M = Cr, Mo, W) complexes led to activate the μ₃-N unit in 1 to afford the new compounds [Ti₃(η⁵-C₅Me₅)₃(μ-O)₄{(NC)M(CO)₅}]₂ [M = Cr (4), Mo (5), W (6)]. Molecular structures of complexes 2-6 have been established by single crystal X-ray analysis.     

Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

Diiron-aminocarbyne complexes with amine or imine ligands: C-N coupling between imine and aminocarbyne ligands promoted by tolylacetylide addition to [Fe2{μ-CN(Me)R}(μ-CO)(CO)(NHCPh2)(Cp)2][SO3CF3]

A terminally coordinated CO ligand in the complexes [Fe₂{μ-CN(Me)R}(μ-CO)(CO)₂(Cp)₂][SO₃CF₃] (R = Me, 1a; R = Xyl, 1b; Xyl = 2,6-Me₂C₆H₃), is readily displaced by primary and secondary amines (L), in the presence of Me₃NO, affording the complexes [Fe₂{μ-CN(Me)R}(μ-CO)(CO)(L)(Cp)₂][SO₃CF₃] (R = Me, L = NH₂Et, 4a; R = Xyl, L = NH₂Et, 4b; R = Me, L = NH₂Prⁱ, 5a; R = Xyl, L = NH₂Prⁱ, 5b; R = Xyl, L = NH₂C₆H₁₁, 6; R = Xyl, L = NH₂Ph, 7; R = Xyl, L = NH₃, 8; R = Me, L = NHMe₂, 9a; R = Xyl, L = NHMe₂, 9b; R = Xyl, = NH(CH₂)₅, 10). In the absence of Me₃NO, NH₂Et gives addition at the CO ligand of 1b, yielding [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(O)NHEt}(Cp)₂] (11). Carbonyl replacement is also observed in the reaction of 1a-b with pyridine and benzophenone imine, affording [Fe₂{μ-CN(Me)R}(μ-CO)(CO)(L)(Cp)₂][SO₃CF₃] (R = Me, L = Py, 12a; R = Xyl, L = Py, 12b; R = Me, L = HNCPh₂, 13a; R = Xyl, L = HNCPh₂, 13b). The imino complex 13b reacts with p-tolylacetylide leading to the formation of the μ-vinylidene-diaminocarbene compound [Fe₂{μ-η¹:η²- CC(Tol)C(Ph)₂N(H)CN(Me)(Xyl){(μ-CO)(CO)(Cp₂)] (15) which has been studied by X-ray diffraction.     

Dibenzothiepins, phthalans and phthalides from 4-heterosubstituted dibenzothiins

The lithiation of 4-heterosubstituted dibenzothiins 1 (phenoxathiin, phenothiazine and thianthrene) with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 7.5% molar) in THF at temperatures ranging from −90 to −78°C gives the corresponding functionalised organolithium intermediate I, which by reaction with different electrophiles [H₂O, D₂O, Bu^tCHO, PhCHO, Ph(CH₂)₂CHO, Me₂CO, Et₂CO, (CH₂)₅CO, (CH₂)₇CO] at the same temperature, followed by hydrolysis, gives the expected functionalised thiols 2. Cyclisation of some thiols 2 under acidic conditions leads to the corresponding seven-membered dibenzo heterocycles 5. In the case of thianthrene 1c, after addition of a carbonyl compound as the first electrophile [MeCHO, Bu^tCHO, Me₂CO, Et₂CO, (CH₂)₅CO], the corresponding intermediate II can be lithiated again and react with a second electrophile. Diols 3 are obtained after hydrolysis when a carbonyl compound [Bu^tCHO, PhCHO, Ph(CH₂)₂CHO, Me₂CO, Et₂CO, (CH₂)₅CO] is used as the second electrophile. Acidic cyclisation of diols 3 gives substituted phthalans 6 in almost quantitative yields. Finally, in the case of using carbon dioxide as the second electrophile, phthalides 4 are obtained after acidic hydrolysis.     

C-C bond formation by cyanide addition to dinuclear vinyliminium complexes

The diiron vinyliminium complexes [Fe₂{μ-η¹:η³-C(R′)C(H)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Me, R′ = SiMe₃ (1a); R = Me, R′ = CH₂OH (1b); R = CH₂Ph, R′ = Tol (1c), Tol = 4-MeC₆H₄; R = CH₂Ph, R′ = COOMe (1d); R = CH₂Ph, R′ = SiMe₃ (1e)) undergo regio- and stereo-selective addition by cyanide ion (from ), affording the corresponding bridging cyano-functionalized allylidene compounds [Fe₂{μ-η¹:η³-C(R′)C(H)C(CN)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (3a-e), in good yields. Similarly, the diiron vinyliminium complexes [Fe₂{μ-η¹:η³-C(R′)C(R′)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = R′ = Me (2a); R = Me, R′ = Ph (2b); R = CH₂Ph, R′ = Me (2c); R = CH₂Ph, R′ = COOMe (2d)) react with cyanide and yield [Fe₂{μ-η¹:η³-C(R′)C(R′)C(CN)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (9a-d). The reactions of the vinyliminium complex [Fe₂{μ-η¹:η³-C(Tol)CHCN(Me)(4-C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4) with NaBH₄ and afford the allylidene [Fe₂{μ-C(Tol)C(H)C(H)N(Me)(C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂] (5) and the cyanoallylidene [Fe₂{μ-C(Tol)C(H)C(CN)N(Me)(C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂] (6), respectively. Analogously, the diruthenium vinyliminium complex [Ru₂{μ-η¹:η³-C(SiMe₃)CHCN(Me)(CH₂Ph)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (7) reacts with to give [Ru₂{μ-η¹:η³-C(SiMe₃)CHC(CN)N(Me)(CH₂Ph)}(μ-CO)(CO)(Cp)₂] (8).Finally, cyanide addition to [Fe₂{μ-η¹:η³-C(COOMe)C(COOMe)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2e) (Xyl = 2,6-Me₂C₆H₃), yields the cyano-functionalized bis-alkylidene complex [Fe₂{μ-η¹:η²-C(COOMe)C(COOMe)(CN)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (10). The molecular structures of 3a and 9a have been elucidated by X-ray diffraction.     

Reactions of 1,8-bis(diphenylphosphino)naphthalene with Os3(CO)12: C-H and C-P bond cleavage reactions

Reactions of Os₃(CO)₁₂ with 1,8-bis(diphenylphosphino)naphthalene (dppn) are described. Crystallographically characterised complexes isolated from a reaction carried out in refluxing toluene are Os₃(μ-H)₂{μ-PPh₂(nap)PPh(C₆H₄)}₂(CO)₆ (1), Os₃(μ-H){μ₃-PPh₂(nap)PPh(C₆H₄)}(CO)₈ (2) and Os₂(μ-PPh₂){μ-PPh₂(nap)}(CO)₅ (3) (nap=1,8-C₁₀H₆), while at r.t. in the presence of ONMe₃, only Os₃(CO)₁₁{PPh₂(1-C₁₀H₇)} (4) was isolated. While 1 and 2 contain ligands formed by metallation of a Ph group of dppn, as found also in complexes obtained from dppn and Ru₃(CO)₁₂, ligands in 3 and 4 are formed by cleavage of a P-nap bond, not found in the Ru series.     

Reductive ring opening of dihydrodibenzothiepine and dihydrodinaphtho-oxepine and -thiepine

The 4,4′di-tert-butylbiphenyl (DTBB)-catalysed lithiation of dihydrodibenzothiepine (1) at −78 °C for 30 min followed by reaction with a carbonyl compound [^tBuCHO, Ph(CH₂)₂CHO, PhCHO, (n-C₅H₁₁)₂CO, (CH₂)₅CO, (CH₂)₇CO, (−)-menthone] at the same temperature leads, after hydrolysis with 3 M hydrochloric acid, to sulphanyl alcohols 2. If after addition of a carbonyl compound as the first electrophile [Me₂CO, (CH₂)₅CO, (−)-menthone], the resulting dianion of type II is allowed to react at room temperature for 30 min, a second lithiation takes place to give an intermediate of type III, which by reaction with a second electrophile [Me₂CO, Et₂CO, (CH₂)₅CO, ClCO₂Et], yields, after hydrolysis, difunctionalised byphenyls 4. The cyclisation of the sulphanyl alcohol 2c under acidic conditions yields the eight-membered sulphur containing heterocycle 3. The lithiation of dihydrodinaphthoheteroepines 7 and 10 with 2.2 equiv of lithium naphthalenide in THF at −78 °C followed by reaction with different electrophiles [H₂O, D₂O, ^tBuCHO, Me₂CO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO] at the same temperature leads, after hydrolysis, to unsymmetrically 2,2′-disubstituted binaphthyls 9 and 12, respectively. When the lithiation is performed with an excess of lithium in the presence of a catalytic amount of DTBB (10% molar), a double reductive cleavage takes place to give the dianionic intermediate VII, which by reaction with different electrophiles [H₂O, Me₂CO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO], followed by hydrolysis with water, yields symmetrically 2,2′-disubstituted binaphthyls 8 and 11. In the case of starting from (R)- or (S)-dihydrodinaphthoheteroepines 7 and 10, these methodologies allow us to prepare enantiomerically pure compounds 8, 11 and 12.     

Models of the iron-only hydrogenase: Reactions of [Fe2(CO)6(μ-pdt)] with small bite-angle diphosphines yielding bridge and chelate diphosphine complexes [Fe2(CO)4(diphosphine)(μ-pdt)]

Reactions of [Fe₂(CO)₆(μ-pdt)] (1) (pdt = SCH₂CH₂CH₂S) and small bite-angle diphosphines have been studied. A range of products can be formed being dependent upon the nature of the diphosphine and reaction conditions. With bis(diphenylphosphino)methane (dppm), thermolysis in toluene leads to the formation of a mixture of bridge and chelate isomers [Fe₂(CO)₄(μ-dppm)(μ-pdt)] (2) and [Fe₂(CO)₄(κ²-dppm)(μ-pdt)] (3), respectively. Both have been crystallographically characterised, 3 being a rare example of a chelating dppm ligand in a first row binuclear system. At room temperature in MeCN with added Me₃NO · 2H₂O, the monodentate complex [Fe₂(CO)₅(κ¹-dppm)(μ-pdt)] (4) is initially formed. Warming 4 to 100 °C leads the slow conversion to 2, while oxidation (on alumina) gives [Fe₂(CO)₅(κ¹-dppmO)(μ-pdt)] (5). With bis(dicyclohexylphosphino)methane (dcpm), heating in toluene cleanly affords [Fe₂(CO)₄(μ-dcpm)(μ-pdt)] (6). With Me₃NO · 2H₂O in MeCN the reaction is not clean as the phosphine is oxidised but monodentate [Fe₂(CO)₅(κ¹-dcpm)(μ-pdt)] (7) can be seen spectroscopically. With 1,2-bis(diphenylphosphino)benzene (dppb) and cis-1,2-bis(diphenylphosphino)ethene (dppv) the chelate complexes [Fe₂(CO)₄(κ²-dppb)(μ-pdt)] (8) and [Fe₂(CO)₄(κ²-dppv)(μ-pdt)] (9), respectively are the final products under all conditions, although a small amount of [Fe₂(CO)₅(κ²-dppvO)(μ-pdt)] (10) was also isolated. Protonation of 2 with HBF₄ affords a cation with poor stability while with the more basic diiron centre in 6 readily forms the stable bridging-hydride complex [(μ-H)Fe₂(CO)₄(μ-dcpm)(μ-pdt)][BF₄] (11) which has been crystallographically characterised.     

A new platform for NCN dimethylamino pincer complexes: Synthesis and structural studies

The reaction of 2,6-(2-{Me₂NCH₂}C₆H₄)₂C₆H₃I (2) with Pd₂(dba)₃ produced the NCN diamine pincer complex [2,6-(2-Me₂{NCH₂}C₆H₄)₂C₆H₃PdI] (3) by an oxidative addition route. The structural analysis of ligand precursor 2 revealed a syn-conformation in the solid state. Single crystal X-ray analysis of complex 3 revealed a conventional square planar geometry about the palladium center and a global C₂ symmetric structure. Variable temperature and concentration NMR spectroscopic studies of complex 3 suggest an equilibrium between 3 and the dinuclear species [{2,6-(2-{Me₂NCH₂}C₆H₄)₂C₆H₃Pd}₂μ²-I]I in CDCl₃ solution. An unusual carbonate complex [{2,6-(2-{Me₂NCH₂}C₆H₄)₂C₆H₃Pd}₃μ³-CO₃]I₃ (4) was also structurally characterized as a minor product during synthesis of 3.     

Assembly and incorporation of a CO2Me group into a bridging vinyliminium ligand in a diiron complex

The diiron complex [Fe₂{μ-к¹(O):η¹(C):η³(C)-C(N(Me)(Xyl))C(H)C(Me)C(O)OMe}(μ-CO)(Cp)₂] (2) has been obtained from the diiron bridging vinyliminium [Fe₂{μ-η¹:η³-C(Me)C(H)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (1; Xyl = 2,5-C₆H₃Me₂) upon treatment with NaH in the presence of CH₂CCMe₂, followed by chromatography on alumina with MeOH as eluent. The reaction consists in the incorporation of a methylcarboxylate unit, assembled from CO and MeO⁻, into the bridging vinyliminium ligand. The resulting complex 2 exhibits a C₄ fragment bridging the two iron centres through the carbonyl oxygen atom and the allylidene moiety.The X-ray molecular structure of 2 has been determined.     

Reaction of the heterometallic cluster Os3Ru(μ-H)2(CO)13 with diphenylphosphine: phosphido-bridged tetrahedral and butterfly clusters

TMNO-activated reaction of the heteronuclear cluster Os₃Ru(μ-H)₂(CO)₁₃ (1) with diphenylphosphine afforded the novel phosphido-bridged clusters Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₁ (2), Os₃Ru(μ-PPh₂)₂(μ-H)₂(CO)₁₀ (3), Os₃Ru(μ-PPh₂)₂(μ-H)₄(CO)₉ (4), and Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₁(PPh₂H) (5). The formation of 2-5 proceeded via P-H bond cleavage in the adduct Os₃Ru(μ-H)₂(CO)₁₂(PPh₂H) (6). Reaction of 2 with PPh₃ afforded the adduct Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₁(PPh₃) (7) and the substituted derivative Os₃Ru(μ-PPh₂)(μ-H)₃(CO)₁₀(PPh₃) (8).     

Ethynylferrocene insertion into Fe-C bond in bridging aminocarbyne diiron complexes: New triiron vinyliminium complexes

The μ-aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCMe)(Cp)₂][SO₃CF₃] (R = Me, 1a; Xyl, 1b; Xyl = 2,6-Me₂C₆H₃) react with ethynylferrocene to give the corresponding bridging vinyliminium complexes [Fe₂{μ-η¹:η³-CN(Me)(R)CHC(Fc)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = Me, 2a; R = Xyl, 2b). Insertion of the ethynylferrocene in the metal-carbyne bond is regiospecific, and leads to the formation of only one isomer.Complexes 2a and 2b undergo hydride addition (by NaBH₄) affording the enaminoalkylidene complex [Fe₂{μ-η¹:η³-C(H)(N(Me)₂)CHC(Fc)}(μ-CO)(CO)(Cp)₂] (3a) and the bis-alkylidene [Fe₂{μ-η¹:η²-C(N(Me)(Xyl))CH₂C(Fc)}(μ-CO)(CO)(Cp)₂] (3b), respectively. Upon treatment with NaH, compounds 2a and 2b undergo fragmentation, affording the 1-metalla-2-aminocyclopenta-1,3-dien-5-one complexes [Fe(CO)(Cp){C(N(Me)(R))}CHC(Fc)C(O)}] (R = Me, 4a; R = Xyl, 4b).The molecular structures of 2b, 3b and 4b have been determined by X-ray diffraction studies.     

Stereochemistry of the insertion of disubstituted alkynes into the metal aminocarbyne bond in diiron complexes

Terminal alkynes (HCCR^′) (R^′=COOMe, CH₂OH) insert into the metal-carbyne bond of the diiron complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCMe)(Cp)₂][SO₃CF₃] (R=Xyl, 1a; CH₂Ph, 1b; Me, 1c; Xyl=2,6-Me₂C₆H₃), affording the corresponding μ-vinyliminium complexes [Fe₂{μ-σ:η³-C(R^′)CHCN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Xyl, R^′=COOMe, 2; R=CH₂Ph, R^′=COOMe, 3; R=Me, R^′=COOMe, 4; R=Xyl, R^′=CH₂OH, 5; R=Me, R^′=CH₂OH, 6). The insertion is regiospecific and C-C bond formation selectively occurs between the carbyne carbon and the CH moiety of the alkyne. Disubstituted alkynes (R^′CCR^′) also insert into the metal-carbyne bond leading to the formation of [Fe₂{μ-σ:η³-C(R^′)C(R^′)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R^′=Me, R=Xyl, 8; R^′=Et, R=Xyl, 9; R^′=COOMe, R=Xyl, 10; R^′=COOMe, R=CH₂Ph, 11; R^′=COOMe, R=Me, 12). Complexes 2, 3, 5, 8, 9 and 11, in which the iminium nitrogen is unsymmetrically substituted, give rise to E and/or Z isomers. When iminium substituents are Me and Xyl, the NMR and structural investigations (X-ray structure analysis of 2 and 8) indicate that complexes obtained from terminal alkynes preferentially adopt the E configuration, whereas those derived from internal alkynes are exclusively Z. In complexes 8 and 9, trans and cis isomers have been observed, by NMR spectroscopy, and the structures of trans-8 and cis-8 have been determined by X-ray diffraction studies. Trans to cis isomerization occurs upon heating in THF at reflux temperature. In contrast to the case of HCCR^′, the insertion of 2-hexyne is not regiospecific: both [Fe₂{μ-σ:η³-C(CH₂CH₂CH₃)C(Me)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Xyl, 13; R=Me, 15) and [Fe₂{μ-σ:η³-C(Me)C(CH₂CH₂CH₃)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Xyl, 14, R=Me, 16) are obtained and these compounds are present in solution as a mixture of cis and trans isomers, with predominance of the former.     

Synthesis and reactivity of η-tetramethylcyclopentadienyl-propenyl rhenium complexes: Molecular structure of [(η:η-C5Me4CH2CHCH2)Re(CO)2]

The fulvene complexes [(η⁶-C₅Me₄CH₂)Re(CO)₂(R)] (1a, RI; 1b, RC₆F₅) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)]⁻. Protonation with HCl at 0 °C produces the hydride complexes [trans-(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)(H)] (2a, RI; 2b, RC₆F₅). Thermolysis of an hexane solution of the iodo-hydride (2a) under a CO atmosphere yields the complex [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₃] (3) and [Re(CO)₅I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η⁵:η²-C₅Me₄CH₂CHCH₂)Re(CO)₂] (4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO)₅(C₆F₅)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe₃, afforded the phosphine derivative [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(PMe₃)] (5). All the complexes were characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopies and mass spectrometry. The molecular structure of 4 has also been determined. The molecule exhibits a formal three-legged piano-stool structure, with two CO groups, and the third position corresponding to the η²-coordination of the propenyl side arm of the η⁵-C₅Me₄ ring.     

Exchange of boryl ligand substituents in Os[B(OEt)2]Cl(CO)(PPh3)2

Reaction between Os[B(OEt)₂]Cl(CO)(PPh₃)₂ and 1,2-ethanediol in the presence of Me₃SiCl (1 equivalent) leads to the tethered boryl complex, Cl(CO)(PPh₃)₂ (1), in which one ethoxy substituent on the boryl ligand is exchanged with one hydroxy group of the 1,2-ethanediol leaving the other OH group available to coordinate to osmium, so giving a six coordinate complex. This formulation is confirmed by crystal structure determination. The same reactants, but with 2 equivalents of Me₃SiCl, lead to the yellow, coordinatively unsaturated complex, OsCl(CO)(PPh₃)₂ (2). Complex (2) adds CO to give OsCl(CO)₂ (PPh₃)₂ (3). Crystal structure determinations of 2 and 3 reveal a very marked difference in the Os-B distances found in the five coordinate complex 2 (2.043(4) Å) and the six coordinate complex 3 (2.179(7) Å). In a reaction similar to that used for forming 2 but with 1,3-propanediol replacing 1,2-ethanediol, the product is OsCl(CO)(PPh₃)₂ (4). The crystal structure for 4 is also reported.     

Tricarbonylrhenium(I) and manganese(I) complexes of 2-(pyrazolyl)-4-toluidine

A series of tricarbonyl rhenium(I) and manganese(I) complexes of the electroactive 2-(pyrazolyl)-4-toluidine ligand, H(pzAn^Me), has been prepared and characterized including by single crystal X-ray diffraction studies. The reactions between H(pzAn^Me) and M(CO)₅Br afford fac-MBr(CO)₃[H(pzAn^Me)] (M = Mn, 1a; Re, 1b) complexes. The ionic species {fac-M(CH₃CN)(CO)₃[H(pzAn^Me)]}(PF₆) (M = Mn, 2a; Re, 2b) were prepared by metathesis of 1a or 1b with TlPF₆ in acetonitrile. Complexes 1a and 1b partly ionize to {M(CH₃CN)(CO)₃[H(pzAn^Me)]⁺}(Br⁻) in CH₃CN but retain their integrity in less donating solvents such as acetone or CH₂Cl₂. Each of the four metal complexes reacts with (NEt₄)(OH) in CH₃CN to give poorly-soluble crystalline [fac-M(CO)₃(μ-pzAn^Me)]₂ (M = Mn, 3a; Re, 3b). The solid state structures of 3a and 3b are of centrosymmetric dimeric species with bridging amido nitrogens and with pyrazolyls disposed trans- to the central planar M₂N₂ metallacycle. In stark contrast to the diphenylboryl derivatives, Ph₂B(pzAn^Me), none of the tricarbonyl group 7 metal complexes are luminescent.     

Synthesis and reactivity of new mono- and dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [Ta(η-C5H4SiMe3)Cl2{NC6Me4-4-(N(SiMe3)2)}]

The reaction of [1,4-{SiMe₃(H)N}₂C₆Me₄] (1) with 2 equivalents of LiBuⁿ followed by the addition of SiMe₃Cl gave the diamine compound [1,4-{(SiMe₃)₂N}₂C₆Me₄] (2). [Ta(η⁵-C₅H₄SiMe₃)Cl₄] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η⁵-C₅H₄SiMe₃)Cl₂}₂(μ-1,4-NC₆Me₄N)] (3), and mononuclear, [Ta(η⁵-C₅H₄SiMe₃)Cl₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacuation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated from the reaction of [Ta(η⁵-C₅H₄SiMe₃)Cl₄] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-ray diffraction studies. [TaCl₃(CH₃CN)₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (5) has been prepared by the reaction of one molar equivalent of TaCl₅ with 2 in a CH₃CN/CH₂Cl₂ solvent mixture. The synthesis of the niobium complexes, [{Nb(η⁵-C₅H₄SiMe₃)Cl₂}₂(μ-1,4-NC₆Me₄N)] (6) and [Nb(η⁵-C₅H₄SiMe₃)Cl₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (7), was achieved in a similar manner to their tantalum analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or lithium dimethylamide, has been studied and the following compounds prepared:[Nb(η⁵-C₅H₄SiMe₃)RCl{NC₆Me₄-4-(N(SiMe₃)₂)}] (R = η⁵-C₅H₄SiMe₃ (8), PhC(NSiMe₃)₂ (9), NMe₂ (10)). In an attempt to form the hetero bimetallic complex, [{Nb(η⁵-C₅H₄SiMe₃)Cl₂}(μ-1,4-NC₆Me₄N){Ta(η⁵-C₅H₄SiMe₃)Cl₂}] (11), the reaction of 7 with [Ta(η⁵-C₅H₄SiMe₃)Cl₄] has been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3 and 6.