Studies on interaction of isocyanide with transition metal complexes : XI. Photochemical reactions of isocyanide complexes of iron

The photochemical reaction of π-C₅H₅Fe(CO)(CNC₆H₁₁)COCH₃ (I) gave the heterocyclic compound π-C₅H₅Fe(CO)[(C=NC₆H₁₁)₂(CH₃)] (II) involving N-coordination to the iron atom. The analogous complex is obtained by the photo-induced reaction of π-C₅H₅Fe(CO)₂CH₃ with C₆H₁₁NC. A similar reaction of π-C₅H₅Fe(CO)[CNC(CH₃)₃]CH₃ with C₆H₁₁NC gave π-C₅H₅Fe(CO)[(C=NC₆H₁₁) {C=N(CH₃)₃}(CH₃)] (IV) involving different N-substituted imino groups. The possible pathways leading to formation of II are discussed. The mass spectra of these complexes were also investigated.     

Some reactions of π-cyclopentadienylbis(triphenylphosphine) rhodium(I)

Reactions of π-cyclopentadienylbis(triphenylphosphine)rhodium(I) (I) with alkyl halides, olefins, acetylenes, carbon disulfide and elementary sulfur have been investigated. Methyl iodide gives the oxidative-addition product [πC₅H₅ Rh(PPh₃)₂CH₃]I but isopropyl iodide produces the alkyl substituted-cyclopentadienyl complex (π-i-C₃H₇C₅H₄)Rh(PPh₃)I₂. Under a nitrogen atmosphere, olefins and acetylenes give compounds of the composition π-C₅H₅ Rh(PPh₃)(L) (L = CH₂—CHCN, CH₂—CHCO₂CH₃, CH₃O₂—CCOO₂CH₃).In the presence of air, however, complexes of the composition π-C₅H₅Rh(L)₂ (L = CH₂—CHCN, CH₂—CHCO₂CH₃, CH₂—C(CH₃)CN) and π-C₅H₅Rh(L)₃ (L = CH₃O₂ CC—CCO₂ CH₃, PhC—CCO₂ CH₃) are formed. The reaction of carbon disulfide or sulfur with (I) also gives the compounds π-C₅H₅Rh(PPh₃)(L) (L = CS₂, CS₃, S₅).     

Photo-degradation studies on di-η5-cyclopentadienyl-dimethyltantalum and some deuterated analogs

The synthesis of (η⁵-C₅H₅)₂Ta(CH₃)₂ in 61% yield from (η⁵-C₅H₅)₂TaCl₂ and methyllithium is described. Photo-degradation of (η⁵-C₅H₅)₂Ta(CH₃)₂ in hydrocarbon solvents results in cleavage of the carbon—tantalum sigma bond. Methane is the major gaseous photo-product. Similar results are obtained in the thermolysis of (η⁵-C₅H₅)₂Ta(CH₃)₂. Deuterium labelling studies indicate that the methyl ligands, the cyclopentadienyl rings and the solvent are all sources of hydrogen in the photochemically-induced formation of methane. The extent to which each source is active in this process cannot be determined, due to an isotopic preference of hydrogen over deuterium. (η⁵-C₅H₅)₂Ta(CH₃)₃ and (C₁₀H₁₀Ta)_x are isolated from the photolysis of (η⁵-C₅H₅)₂Ta(CH₃)₂ in pentane. Irradiation of (η⁵-C₅H₅)₂Ta(CH₃)₂ in the presence of carbon monoxide results in formation of (η⁵-C₅H₅)₂Ta(CO)CH₃.     

Synthesis and reactions of substituted zirconocene and hafnocene dimethyls and the corresponding dihydrides

Hydrogenolysis of M(CH₃)₂(M = Zr, Hf) bonds gives novel substituted zirconocene and hafnocene dihydrides. The use of the optically active complex [η⁵-C₆H₅C★H(CH₃)C₅H₄] (η⁵-C₅H₅)Zr(CH₃)₂ as a catalyst in homogeneous hydrogenation of prochiral alkenes is reported.     

13C relaxation mechanisms in methyl-transition metal complexes: high barriers to rotation about metalcarbon σ bonds

¹³C T₁ and η(CH) have been measured for the methyl carbon in cis-Os(CO)₄(CH₃)₂, (π-C₅H₅)Fe(CO)₂CH₃, (π-C₅H₅)Mo(CO)₃CH₃ and (π-C₅H₅)₂Zr(CH₃)₂. From this data, barriers to methyl rotation are estimated to be 4.4 ± 0.7, 5.4 ± 2, > 6, and > 6 kcal/mol, respectively. It appears that such barriers can be substantial even in uncrowded molecules.     

Photo-degradation studies on Di-η5-Cyclopentadienyldimethylvanadium,Di-η5-Cyclopentadienylmethylvanadium,Di-η5-Cyclopentadienyldimethylniobium,and some deuterated analogs

The photolysis of alkyl metallocene derivatives of vanadium and niobium in hydrocarbon solvents results in cleavage of the carbon—metal σ-bond. In the cases of (η⁵-C₅H₅)₂VCH₃ and (η⁵-C₅H₅)₂Nb(CH₃)₂, only methane (>99%) is produced photochemically. (η⁵-C₅H₅)₂V(CH₃)₂, prepared on a convenient new synthesis from (η⁵-C₅H₅)₂VCl₂ and methyllithium in toluene, degrades under photochemical conditions to yield both methane and ethane in a 2 : 1 ratio. The ethane arises from intra- and intermolecular methyl dimerization. Deuterium labeling studies have shown that the methyl group, the cyclopentadienyl ring, and the solvent are all sources of hydrogen in the formation of methane in these photolyses. The extent to which each source participates in the hydrogen abstraction process cannot be quantitatively determined because of the influence of an isotope effect. Chemical reactions with carbon monoxide during the photolyses give low yields of (η⁵-C₅H₅)V(CO)₄ from (η⁵-C₅H₅)₂VCH₃ or (η⁵-C₅H₅)₂V(CH₃)₂, and of (η⁵-C₅H₅)₂Nb(CO)CH₃ from (η⁵-C₅H₅)₂Nb(CH₃)₂.     

Dendritic β-diketiminato titanium and zirconium complexes: synthesis and ethylene polymerisation

The cyclopentadienyl(β-diketiminato)titanium and zirconium chlorides (η⁵-C₅H₅)MCl₂(CH(C(NC₆H₄-4-OR)CH₃)₂) (M = Ti (4-dend), Zr (5-dend)), where R corresponds to the first generation carbosilane dendron (dendritic wedge) Si(CH₂CH₂SiMePh₂)₃, have been synthesised. After activation with methylaluminoxane, the activity of 4-dend and 5-dend as catalysts for ethylene polymerisation has been determined and compared with that of the non-dedritic counterpart (η⁵-C₅H₅)MCl₂(CH(C(NC₆H₅)CH₃)₂) (M = Ti (4), Zr (5)).     

Pyrolysis of metallocene complexes (ηC5H4R)2MR: An organometallic route to metal carbide (MC) materials (M = Ti,Zr, Hf)

The following compounds were prepared and their pyrolysis in a stream of argon was studied: (η⁵-C₅H₅)₂Ti(C?CC₆H₅)₂, (η⁵-C₅H₄SiMe₃)₂-Ti(SH)₂, [(η⁵-C₅H₅)Ti(μ-CH₂)]₂, (η⁵-C₅H₅)₂ZrR₂-(R?CH₂, CH₂C₆H₅, N(CH₃)₂), (η⁵-C₅H₄CH₃)₂-Zr(C?CC₆H₅)₂, [(η⁵-C₅H₄SiMe₃)₂Zr(μ-S)]₂, [(η⁵-C₅H₄SiMe₃)₂Hf(μ-S)]₂ and (η⁵-C₅H₄SiMe₃)₂Hf-(C?CC₆H₅)₂. The products of bulk pyrolysis of these materials were formed in 20–40% yield, based on the charged sample weight, and consisted mainly of titanium carbide together with small amounts of amorphous carbon.     

Homo- and hetero-binuclear ansa-metallocenes of the group 4 transition metals as homogeneous co-catalysts for the polymerisation of ethene and propene

The compounds [M{(CH₂)₄C(η-C₅H₄)₂}(η-C₅H₅)Cl] (M=Zr^*, Hf), [M{(CH₂)₄C(η-C₅H₄)₂}(η-C₅H₅)Me] (M=Zr, Hf), [(η-C₅H₅)MCl₂{(CH₂)₄C(η-C₅H₄)₂}MCl₂(η-C₅H₅)] (M=Zr, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)(η-C₉H₆)}ZrCl₂(η-C₅H₅)], [(η-C₅H₅)MMe₂{(CH₂)₄C(η-C₅H₄)₂}MMe₂(η-C₅H₅)] (M=Zr, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)₂}HfCl₂(η-C₅H₅)], [(η-C₅H₅)MCl₂{(CH₂)₄C(η-C₅H₄)₂}Rh(η-C₈H₁₂)] (M=Zr^*, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)₂}TiCl₃], [(η-C₅H₅)ZrMe₂{(CH₂)₄C(η-C₅H₄)₂}HfMe₂(η-C₅H₅)], [(η-C₅H₅)MMe₂{(CH₂)₄C(η-C₅H₄)₂}Rh(η-C₈H₁₂)] (M=Zr^*, Hf) have been prepared and characterised. ^* indicates the crystal structure has been determined. Their catalytic properties for ethene and propene polymerisation have been explored.     

Bonding and reactivity in π-allyl—metal compounds

The π-allyl group of π-C₃H₅Co(CO)₃ has two angles of tilt, one of which (from semi-empirical molecular orbital calculations) is stabilised principally by the influence of the C(p_v) orbitals of the terminal carbon atoms, which form part of the σ-framework of the π-allyl group, and the other of which is stabilised by a balance between bonding orbital components of the central and terminal carbon atoms. The Co(CO)₃ moiety has asymmetric bonding, with one CO group more weakly bonded to the metal atom. The asymmetric bonding of the Co(CO)₃ moiety is primarily caused by the electronic character of the π-allyl group, but is significantly influenced by the magnitude of the τ-tilt angle of the π-allyl group. The relatively high reactivity of π-C₃H₅Co(CO)₃, compared with the reactivity of π-C₃H₅Fe(CO)₂NO, Co(NO)(CO)₃, or Ni(CO)₄, is explained by the relatively weak bonding of a CO group to the metal atom and a possible explanation of the anomalous relative rates of the reactions of π-C₃H₄RCo(CO)₃ (R = H, 1-CH₃, 2-CH₃, 1-Cl, 2-Cl) with P(C₆H₅)₃ is indicated.The angles of tilt of the π-allyl group and the asymmetric bonding of the π-cyclopentadienyl moiety in [π-C₃H₄Ni(π-C₅H₅)]₂ are caused by factors similar to those in π-C₃H₅Co(CO)₃.     

Reactions of π-benzeneruthenium(II) complexes with alkylating reagents

The compounds (π-C₆H₆)Ru(R)Cl(PPh₃) (RCH₃, C₆H₅), (π-C₆H₆)RuCl(π-C₃H₅) and [(π-C₆H₆)Ru(π-C₅H₅)]Cl are described. The ³¹P NMR spectra of a series of tertiary phosphine complexes of the π-benzeneruthenium system are also reported.     

New alkenyl-substituted group 4 C-ansa-metallocene complexes. Reactivity of the substituent at the carbon ansa bridge

The allyl-substituted group 4 metal complexes [M{(R)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti, R = CH₂CHCH₂, (2); R = CH₂C(CH₃)CH₂ (3); M = Zr, R = CH₂CHCH₂ (4), R = CH₂C(CH₃)CH₂ (5)] have been synthesized by the reaction of allyl ansa-magnesocene derivatives and the tetrachloride salts of the corresponding transition metal. The dialkyl complexes ] [M = Ti, R = CH₂=CHCH₂, R′ = Me (6), R′ = CH₂Ph (7); R = CH₂C(CH₃)CH₂, R′ = Me (8), R′ = CH₂Ph (9); M = Zr, R = CH₂CHCH₂, R′ = Me (10), R′ = CH₂Ph (11); R = CH₂C(CH₃)CH₂, R′ = Me (12), R′ = CH₂Ph (13)] have been synthesized by the reaction of the corresponding ansa-metallocene dichloride complexes 2-5 and two molar equivalents of the alkyl Grignard reagent. Compounds 2-5 reacted with H₂ under catalytic conditions (Wilkinson’s catalyst or Pd/C) to give the hydrogenation products [M{(R)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti and R = CH₂CH₂CH₃ (14) or R = CH₂CH(CH₃)₂ (15); M = Zr and R = CH₂CH₂CH₃ (16) or R = CH₂CH(CH₃)₂ (17)]. The reactivity of 2-5 has also been tested in hydroboration and hydrosilylation reactions. The hydroboration reactions of 3, 4 and 5 with 9-borabicyclo[3.3.1]nonane (9-BBN) yielded the complexes [M{(9-BBN)CH₂CH(R)CH₂CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti and R = H (18); M = Zr and R = H (19) or R = CH₃ (20)]. The reaction with the silane reagents HSiMe₂Cl gave the corresponding [M{ClMe₂SiCH₂CHRCH₂CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti and R = H (21); M = Zr and R = H (22) or R = CH₃ (23)]. The reaction of 22 with t-BuMe₂SiOH produced a new complex [Zr{t-BuMe₂SiOSi(Me₂)CH₂CH₂CH₂CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (24) through the formation of Si-O-Si bonds. On the other hand, reactivity studies of some zirconocene complexes were carried out, with the insertion reaction of phenyl isocyanate (PhNCO) into the zirconium-carbon σ-bond of [Zr{(n-Bu)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}₂Me₂] (25) giving [{(n-Bu)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)]}Zr{Me{κ²-O,N-OC(Me)NPh}] as a mixture of two isomers 26a-b. The reaction of [Zr{(n-Bu)(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}(CH₂Ph)₂] (27) with CO also provided a mixture of two isomers [{(n-Bu)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)]}Zr(CH₂Ph){κ²-O,C-COCH₂Ph}] 28a-b. The molecular structures of 4, 11, 16 and 17 have been determined by single-crystal X-ray diffraction studies.     

Complexes du titane et du zirconium contenant les ligands cyclopentadienyldiphenylphosphine et cyclopentadienylethyldiphenylphosphine: acces a des structures heterobimetalliques

Reactions of Ph₂P(CH₂)_n(C₅H₄)Li, (n = 0, 2), with MCl₄ or CpTiCl₃ (M = Ti, Zr; Cp = η⁵-C₅H₅) form Cl₂M[(η⁵-C₅H₄)(CH₂)_nPPh₂]₂ or Cl₂CpTi[(η⁵-C₅H₄)-(CH₂)₂PPh₂] in good yields. Chemical reduction with Al, or electrochemical reduction of these complexes, under CO, are described. The titanium(IV) and zirconium(IV) derivatives react with metal carbonyls (Mo(CO)₆, Cr(CO)₆, Fe(CO)₅, Mo(CO)₄(C₈H₁₂)) under formation of new heterobimetallic complexes. Reduction with Al of Cl₂CpTi[(η⁵-C₅H₄)(CH₂)₂PPh₂]Mo(CO)₅ under CO results in a new heterobimetallic species containing low valent titanium. Both complexes Cl₂M[(η⁵-C₅H₄)(CH₂)₂PPh₂]₂ (M = Ti, Zr) react with [Rh(μ-Cl)(CO)(C₂H₄)]₂ to yield {RhCl(CO)(Cl₂M[(η⁵-C₅H₄)(CH₂)₂PPh₂]₂)}x, which is assumed to be a dimer, in which the titanium or the zirconium compounds act as bridging diphosphine ligands between the rhodium atoms.     

Hydride complexes of titanium and zirconium attached to SiO2 as hydrogenation catalysts

Catalysts obtained by interacting Ti(CH₂C₆H₅)₄ or Zr(π-C₃H₅)₄ with the surface of SiO₂ and treated with hydrogen possess a very high activity with respect to hydrogenation of benzene and cyclohexene. This activity is commensurable with that of supported Group VIII metals. The catalysts were studied by chemisorption, thermodesorption and EXAFS methods, and were shown to contain anchored hydride complexes of Ti and Zr, whose content can be controlled by varying the temperature of their treatment with hydrogen. A quantitative correlation exists between the specific activity of the catalysts under consideration in hydrogenation reactions and the content of hydride complexes in these catalysts.     

Derivatives of cyclooctatetraenecyclopentadienyl-titanium containing substituents in the five-membered ring

The syntheses of some substituted cyclooctatetraenecyclopentadienyl-titanium compounds are described, viz: (h⁸-C₈H₈)(h⁵-R)Ti with R = C₅H₄CH₃, C₅H₄C(CH₃)₃, C₅H₄Si(CH₃)₃, indenyl (= Ind) and fluorenyl (= Flu). The compounds have been prepared by reaction of [(h⁸-C₈H₈)TiCl·THF]₂ with RNa in ether solution. The paramagnetic compounds are thermally stable to ca. 350°, but they are sensitive to air and water. The IR spectra and dipole moments of the compounds are given. The mass spectra of the complexes (h⁸-C₈H₈)(h⁵-C₅H₅)Ti, (h⁸-C₈H₈)(h⁵-Ind)Ti and (h⁸-C₈H₈)(h⁵-Flu)Ti indicate weakening of the Tih⁵R bond-strength in this sequence.     

Reactions of nickelocene with lithium and magnesium alkyls containing β-hydrogen atoms

The reaction of nickelocene with BrMgR, where R=CH₂CH(CH₃)C₆H₅, C₂H₅, (CH₂)₇CH₃ and CH₂CH₂CH₃, have been studied. It was found that the presence of β-hydrogen in R did not cause the total splitting of the carbon–nickel bond but alkylidynetrinickel clusters were formed. It is the first example of the synthesis of alkylidynetrinickel clusters (NiCp)₃CR′ from the organonickel species possessing β-hydrogen. Besides trinickel clusters, the following compounds were always formed in all the studied reactions: (NiCp)₄H₂, (NiCp)₆, CpNi(η³-C₅H₇) and (NiCp)₂(μ-C₅H₆). The structure of (NiCp)₃CCH(CH₃)Ph has been determined by a single-crystal X-ray diffraction study.     

Synthesis and Spectra of Cationic Bis(tertiary phosphine) derivatives of cycloheptatrienyliummolybdenum and cyclopentadienyliron complexes

Reaction of [(η-C₇H₇)Mo(CO)₃][PF₆] and [(η-C₅H₅)Fe(CO)₂CH₃CN][PF₆] with ditertiary phosphine ligands afforded products of three types; the monosubstituted complexes [(Ring)M(CO)₂Ph₂P(CH₂)_nPPh₂][PF₆] (Ring = η-C₇H₇, M = Mo, N = 1; Ring = η-C₅H₅, M = Fe, N = 1 and 2), the chelated complexes [(Ring)M(CO)Ph₂P(CH₂)_nPPh₂][PF₆] (Ring = η-C₇H₇, M = Mo, N = 1 and 2; Ring = η-C₅H₅, M = Fe, N = 1 and 2), and the dinuclear complex [{(η-C₇H₇)Mo(CO)₂}₂ -μ- Ph₂PCH₂CH₂PPh₂][(PF₆)₂]. Spectroscopic properties, including ³¹P NMR, are reported.     

Ruthenium(II) complexes with ferrocene-modified arene ligands: synthesis and electrochemistry

A series of arene-ruthenium complexes of the general formula [RuCl₂{η⁶-C₆H₅(CH₂)₂R}L] with R=OH, CH₂OH, OC(O)Fc, CH₂OC(O)Fc (Fc=ferrocenyl) and L=PPh₃, (diphenylphosphino)ferrocene, or bridging 1,1^′-bis(diphenylphosphino)ferrocene, have been synthesized. Two synthetic pathways have been used for these ferrocene-modified arene-ruthenium complexes: (a) esterification of ferrocene carboxylic acid with 2-(cyclohexa-1,4-dienyl)ethanol, followed by condensation with RuCl₃ · nH₂O to afford [RuCl₂{η⁶-C₆H₅(CH₂)₂OC(O)Fc}]₂, and (b) esterification between ferrocene carboxylic acid and [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}L] to give [RuCl₂{η⁶-C₆H₅(CH₂)₃OC(O)Fc}L]. All new compounds have been characterized by NMR and IR spectroscopy as well as by mass spectrometry. The single-crystal X-ray structure analysis of [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] shows that the presence of a CH₂CH₂CH₂OH side-arm allows [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] to form an intramolecular hydrogen bond with a chlorine atom. The electrochemical behavior of selected representative compounds has been studied. Complexes with ferrocenylated side arms display the expected cyclic voltammograms, two independent reversible one-electron waves of the Ru(II)/Ru(III) and Fe(II)/Fe(III) redox couples. Introduction of a ferrocenylphosphine onto the ruthenium is reflected by an additonal reversible, one-electron wave due to ferrocene/ferrocenium system which is, however, coupled with the Ru(II)/Ru(III) redox system.     

Synthesis and reaction chemistry of 4-nitrile-substituted NCN-pincer palladium(II) and platinum(II) complexes (NCN = [NC-4-C6H2(CH2NMe2)2-2,6])

Nitrile-functionalized NCN-pincer complexes of type [MBr(NC-4-C₆H₂(CH₂NMe₂)₂-2,6)] (6a, M = Pd; 6b, M = Pt) (NCN = [C₆H₂(CH₂NMe₂)₂-2,6]⁻) are accessible by the reaction of Br-1-NC-4-C₆H₂(CH₂NMe₂)₂-2,6 (2b) with [Pd₂(dba)₃ · CHCl₃] (5a) (dba = dibenzylidene acetone) and [Pt(tol-4)₂(SEt₂)]₂ (5b) (tol = tolyl), respectively. Complex 6b could successfully be converted to the linear coordination polymer {[Pt(NC-4-C₆H₂(CH₂NMe₂)₂-2,6)](ClO₄)}_n (8) upon its reaction with the organometallic heterobimetallic π-tweezer compound {[Ti](μ-σ,π-CCSiMe₃)₂}AgOClO₃ (7) ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti).The structures of 6a (M = Pd) and 6b (M = Pt) in the solid state are reported. In both complexes the d⁸-configurated transition metal ions palladium(II) and platinum(II) possess a somewhat distorted square-planar coordination sphere. Coordination number 4 at the group-10 metal atoms M is reached by the coordination of two ortho-substituents Me₂NCH₂, the NCN ipso-carbon atom and the bromide ligand. The NC group is para-positioned with respect to M.     

Metallcarbonyl-Synthesen,XIV. Neuartige Vanadium-, Niob- und Tantal-Komplexe mit Wasserstoff-Brücken

Syntheses of Metal Carbonyls, XIV. Novel Vanadium, Niobium, and Tantalum Complexes Having Hydrido Bridges The novel homo- and heterodinuclear organometallic μ-hydrido compounds 3a – c of vanadium, niobium, and tantalum have been synthesized by light-induced reactions of the hydridoniobium complex (η⁵-C₅H₅)₂NbH₃ ( 1 ) with the half-sandwich complexes (η⁵-C₅H₅)M(CO)₄ ( 2a : M = V; 2b : M = Nb; 2c : M = Ta). These compounds have the general composition L_xM – H – Nb(CO)(η⁵-C₅H₅)₂. The formation of the M – H – Nb moieties is a dark-reaction preceded by two photoreactions that are independent from each other elimination of CO from 2a – c and elimination of H₂ from 1 , with the extruded carbon monoxide being transfered to the (η⁵-C₅H₅)₂NbH fragment; subsequent fixation of the species (η⁵-C₅H₅)₂Nb(CO)H thus generated to the photogragments (η⁵-C₅H₅)M(CO)₃ results in donor stabilization of these latter groups. The structural architecture of the derivatives 3a und b was established by X-Ray diffraction. The hydrogen bridges are to be considered as three-center two-electron functions that are responsible for a serious lengthening of the otherwise by at least 40 pm shorter metal-to-metal distances amounting to 371.3 pm in 3a and 373.3 pm in 3b (mean values).