Maarten W. Kokkes

Photochemistry of metal—metal bonded complexes: III. MLCT photolysis of (CO)5MM′(CO)3(α-diimine) (M, M′ = Mn, Re) in 2-Me-THF and THF at 293 K; Evidence of photocatalytic formation of [(Mn(CO)3(α-diimine)(P(n-Bu)3)]+ [M(CO)5] - upon photolysis in the presence of P(n-Bu)3

Abstract Complexes op the type (CO) 5 MM′(CO) 3 (α-diimme) (M, M′ = Mn, Re) were photolyzed in 2-Me-THF at 293 K in the absence and presence of PR 3 by irradiation in the low energy M′ → α-diimine charge transfer band. In most cases the primary photoprocess appeared to be homolysis of the (M-M′) metal—metal bond. In the absence of PR 3 the radicals formed react with each other to give M 2 (CO) 10 and M′ 2 (CO) 6 (α-diimine) 2 . It is shown that the stabilities of these M′ 2 (CO) 6 (α-diimine) 2 complexes depend on the α-diimine ligand used. In the presence of PR 3 various reactions are observed, depending on the complex and the PR 3 ligand used. Thus, photolysis of (CO) 5 MnRe(CO) 3 (α-diimine) in the presence of PPh3 or P(n-Bu) 3 gives Mn 2 (CO) 10 and a reaction product of Re 2 (CO) 6 (α-diimine) 2 . However, (CO) 5 MnMn(CO) 3 (α-diimine) in the presence of PPh 3 gives Mn 2 (CO) 8 (PPh 3 ) 2 instead of Mn 2 (CO) 10 . A remarkable reaction is observed when a (CO) 5 MnMn(CO) 3 (α-diimine) complex is photolyzed in the presence of the basic phosphine P(n-Bu) 3 the ionic compound [Mn(CO) 3 (α-diimine)(P(n-Bu) 3 )] + [Mn(CO) 5 ] − being formed as the result of electron transfer from the radical Mn(CO) 3 (α-diimine)(P(n-Bu) 3 ) to Mn(CO) 5 and (CO) 5 MnMn(CO) 3 (α-diimine). This reaction is a photocatalyzed chain reaction with φ ∼ 10. All these reactions involve initial homolysis of the metal—metal bond. Only in the case of (CO) 5 ReMn(CO) 3 (R-DAB) in the presence of PR 3 was a carbonyl group of the Mn(CO) 3 (R-DAB) fragment photosubstituted. The mechanisms of the reactions are discussed.

Synthesis andmolecular geometry of [trans-PtCl2PBu3]2 (di-t-Bu-diimine) containing a s,s-N,N' bridging diimine with a planar anti-(trans-P-Pt-NCCN-Pt-P-trans)-skeleton

Abstract Complexes of the type [MCl 2 XR′ 3 ] 2 R-dim (M = Pd or Pt; XR′ 3 = arsine or phosphine) are formed in almost quantitative yield in the reactions of [MCl 2 XR′ 3 ] 2 with α-diimine ( 1 1 molar ratio Pt-dimer/R-dim). An X-ray study of [PtCl 2 PBu 3 ] 2 t-Bu-dim [Z = 2, a = 11.4540(11), b = 16.1169(7), c = 12.9202(12) A and β = 99.82(1); R = 5.9%] reveals a structure consisting of two planar trans-PtCl 2 P-units bridged by a planar NCCN skeleton in anti-configuration [CC 1.48(2), CN 1.27(3), NPt 2.214(10) A]. As a consequence of the orthogonal position of the platinum coordination plane and the NCCN plane the β-imine proton resides a short distance from the platinum atom (about 2.6 A). The structure in solution has been determined by 1 H, 13 C, 31 P and 195 Pt NMR spectroscopy. The observed spectra point to retention of the structural features in solution as evidenced by a large down field shift of the imine protons, e.g. 9.58 ppm and an AA′MM′ pattern in [PdCl 2 PEt 3 ] 2 t-Bu-dim. The present compounds are the first examples of complexes which contain a σ,σ′-N,N′ planar bridging diimine ligand as a general structural feature.

Structural and spectroscopic properties of [(CO)5MM′ (CO)3(R-DAB)] (M,M′=Mn,Re; R-DAB=1,4-diaza-1,3-butadiene complexes. X-ray structure of [(CO)5ReMn(CO)3-(i-Pr-DAB)] and infrared and resonance Raman spectra of [(CO)5MM′(CO)3(R-DAB)]

Abstract The X-ray structure of the title compound has been determined by the heavy-atom method and refined by means of block-diagonal least-squares calculations from 2116 independent reflections. The crystals are monoclinic, space group P 2 Vc with unit cell dimensions a = 18.494(3), b = 7.502(2), c = 16.52(2) A, β = 113.760(6)° and Z = 4. The final R value was 0.037. The complex has an octahedral geometry and the CO ligands of the Re(CO) 3 and Mn(CO) 3 (i-Pr-DAB) moieties are in staggered positions. The Mn-Re bond length is 3.012(2) A and the MnN bond lengths are 1.994(9) and 2.003(9) A. The infrared and resonance Raman (RR) spectra obtained by excitation into the lowest electronic absorption band, are reported. A tentative assignment for the CO-stretching vibrations is presented based on their solvent and temperature dependence. The RR spectra of (CO) 3 MM′(CO) 3 (i-Pr-DAB) (M,M′=Mn, Re) taken from N 2 -matrices at 10 K are very weak, which means that the equilibrium conformation of these complexes hardly changes upon going from the ground state to the excited state. These RR spectra are discussed considering the electronic structure of these complexes.

He(I) and He(II) photoelectron spectra of mononuclear transition metal carbonyl complexes containing a 1,4-diaza-1,3-butadiene ligand

Abstract He(I) and He(II) photoelectron spectra have been recorded for the following mononuclear transition metal carbonyl complexes containing symmetrically 1,4-disubstituted 1,4-diaza-1,3-butadienes, RNC(R′)C(R″)NR, d6 [M(CO)4(RNCHCHNR)] (M = Cr, W, R = i-Pr; M = Mo, R = t-Bu) and [ReCl(CO)3(i-Pr-NCHCHN-i-Pr)], d8 [M(CO)3(RNCR′CR″NR)] (M = Fe, R = t-Bu, n-Bu, c-Hex, R′ = R″ = H; M = Fe, R = n-Bu, R′ = R″ = Me; M = Ru, R = i-Pr2CH, R′= R″ = H) and [Fe(t-BuNCHCHN-t-Bu)2], and d10 [Ni(CO)2(t-BuNCHCHN-t-Bu)] and [Ni(t-BuNCHCHN-t-Bu)2]. The observed vertical ionization energies (IEs) are tabulated and assigned to metal d orbitals and ligand systems on the basis of the results of semi-empirical molecular orbital (MO) calculations, He(I)/He(II) intensity ratios, and comparisons with related molecules (trend effects). The weighted average IE of the metal d orbitals in each R-DAB complex ( IE ′d) is lower than that of the corresponding unsubstituted metal carbonyl complex ( IE d). The values of ΔIEd (= IE ′d - IE d) are −1.54 eV for the d6 complexes, −1.80 eV for the d8 system and −2.09 eV for the d10 compound. This means that ΔIEd increases by the same amount on going from d6 to d8 complexes (0.26 eV) as it does on going from d8 to d10 complexes (0.29 eV). Replacement of two CO groups by a second RNCHCHNR ligand leads to a further lowering of the weighted average IE of the d orbitals (−0.5 eV) which is significantly less than that found for the first substitution.

Spectroscopic and theoretical studies of [Fe(CO)3(1,4-diaza-1,3-butadiene)] complexes; X-ray structure and magnetic circular dichroism and resonance-Raman spectra of [1,2-bis(2′,6′-di-isopropylphenylimino)ethane-NN′]tricarbonyliron

The X-ray structure of the title compound has been determined by the heavy-atom method and refined by means of block-diagonal least-squares calculations from 5 537 independent reflections. The crystals are monoclinic, space group P21/n, with unit-cell dimensions a= 18.422(4), b= 16.155(3), c= 9.966(3)A, β= 90.40(3)°, and Z= 4. The final R value was 0.044. The compound has a distorted square pyramidal structure with Fe–N bond lengths of 1.929(2) and 1.926(3)A. Molecular-orbital (m.o.) calculations reveal a low-lying lowest unoccupied molecular orbital which has substantial π*(α-di-imine) character. Most low-lying transitions are directed to this orbital. M.c.d., electronic absorption, and resonance-Raman (r.R.) spectra, obtained by excitation into the lowest electronic absorption bands, are reported. They give evidence for several electronic transitions in the low-lying absorption band. Two of these transitions are pseudo-degenerate, leading to an A term in the m.c.d. spectrum. The r.R. spectra are very weak which means that the bonds of the complex are hardly affected by the charge-transfer transitions. The spectra show that the complex relaxes to another conformation in the excited state. Differences between the m.o. calculations and the r.R. spectra are discussed.

A mechanistic study of the photochemistry of tricarbonyl(1-aza-1,3-butadiene)iron complexes [Fe(CO)3(R′NCHCHCHPh)] in CH4 matrices at 10 K and in solution at 293 K

Abstract The photochemistry has been studied of the complexes [Fe(CO)3(R1, Ph-ABD)] (R1,Ph-ABD represents R1NCHCHCHPh; 1R1,4Ph-1-aza-1,3-butadiene) both in a CH4 matrix at 10 K and in solution at 293 K. Matrix photolysis of [Fe(CO)3(i-Pr,Ph-ABD)] causes breaking of the ironolefin bond with formation of the 16-electron species [Fe(CO)3(]gs-N-i-Pr,Ph-ABD)]. In solution the R1Ph-ABD ligand is replaced photochemically by other R1,Ph-ABD molecules and by R-DAB (R-DAB = 1,4-diaza-1,3-butadiene; RNCHCHNR). Photolysis in the presence of PR3 results in the formation of [Fe(CO)2(R1,Ph-ABD)(PR3)], [Fe(CO)3(PR3)2] and [Fe(CO)4(PR3)]. The relative amounts of these photoproduct depend on the PR3 concentration, on the R1,Ph-ADB ligand used, and on the polarity of the solvent. A mechanism is proposed in which the product of the matrix photolysis is assumed to be the primary photoproduct of the photosubstitution reactions.

Spectroscopic properties and photochemistry of [Fe(CO)3(1,4-Diazabuta-1,3-diene)] complexes

Abstract Different photochemical reactions are found for [Fe(CO) 3 (dab)] (dab = 1,4-diazabuta-1,3-diene) in matrices at 10 K and in solutions at room temperature. Matrix photolysis results in loss of CO via an intermediate in which the dab-ligand is π,π-coordinated to the metal, whereas photolysis in solution leads to CO-substitution after breaking of a metal-nitrogen bond. This behaviour is discussed in relationship to the spectroscopic properties of [Fe(CO) 3 (dab)].

σ,σ′-N,N′ bridging and σ,σ-N,N chelating α diimines. Molecular geometries of [PtCl2PBu3]2(t-BuNCHCHNBu-t) and PtCl2(styrene)(t-BuNCHCHNBu-t)

X-ray structure analysis of [PtCl 2 PBu 3 ] 2 (t-BuNCHCHNBu-t) has shown the presence of σ,σ′- N , N ′-bonded diimine, which bridges in the anti configuration two planar trans -PtCl 2 PBu 3 N moieties. The crystal structure of PtCl 2 (styrene)(t-BuNCHCHNBu-t) contains a unidentate-bonded styrene molecule in the equatorial position of a trigonal bipyramidal arrangement with the phenyl ring bent back by 27°.

Photochemistry of tricarbonyl(α-di-imine)iron complexes. New mechanistic aspects for CO photosubstitution in solution and evidence for π,π-co-ordination of 1,4-diaza-1,3-butadiene ligands in matrices at 10 K

The metal-to-ligand charge-transfer photochemistry of [Fe(CO)3(α-di-imine)] has been studied in detail. For [Fe(CO)3L](L = 1,4-diaza-1,3-butadiene, RNCH–CHNR) CO photosubstitution takes place with high quantum yield (Φ≃ 0.2) in solution via a partial dissociation of L. In matrices at 10 K, a changeover from σ,σ-N,N′- to π,π-co-ordination is found as primary step in the photolysis of [Fe(CO)3L] complexes. The resulting [Fe(CO)3(π,π-L)] decomposes thermally to a [Fe(CO)2(σ,σ-N,N′-L)] fragment with simultaneous release of CO. For [Fe(CO)3(dpipy)][dpipy = 2-(2′,6′-di-isopropylphenylimino)pyridine] no π,π-co-ordination is observed. A 13CO-labelling force-field calculation has been performed for a [Fe(CO)3L] complex and its photolysis product [Fe(CO)2(σ,σ,-N,N′-L)], showing two structurally different conformers of the latter product. The different photochemical behaviour in solution and in a matrix is discussed and a mechanism is proposed for the photosubstitutional reactions in solution.

Isostructural triazenido complexes of first row transition metals. Part 2. Synthesis and properties of [(η5-C5H5)L(RN3R)CoIII]PF6, L = PEt3, PPh3, P(OMe)3 and P(OPh)3

SummaryThe synthesis and properties of the [(η5-C5H5)L(RN3R)CoIII]PF6 complexes, with L = PEt3, PPh3, P(OMe)3 or P(OPh)3, are reported. A six coordinate configuration containing a chelating triazenido ligand is proposed which is isostructural with the known complexes of iron and nickel.The spectroscopic properties of the isoelectronic Co and Fe complexes, (η5-C5H5)L(RN3R)M, are compared in relation to the charge on the central metal atom. The complex with L = CO could not be prepared, but the carbonyl inserted product (η5-C5H5)(L{RNNN(R)C(O)}Co was isolated. In one of the reactions, the novel ring-bound triphenylphosphine complex, [η5-C5H5)(η5-C5H4PPh3)CoIII](PF6)2, was isolated as a side product. The mechanism of this reaction is discussed.