Beatriz Oelckers

cis–trans Isomerisation of CpRe(CO)2(H)(ArF)(ArF= C6FnH5−n; n= 0–5) is the rate determining step in C–H activation of fluoroarenes: a DFT study

Density functional calculations have been used to examine the reaction of {CpRe(CO)2} with fluorobenzenes C6FnH6−n (n = 0–5). Two classes of product have been observed experimentally (using Cp or Cp*): (a) coordination of the arene in an η2 fashion and (b) C–H activation to form a hydrido–aryl complex. Increasing the number of fluorines on the arene ring was shown to favour C–H activation. The thermodynamic and kinetic (reaction path) aspects of these transformations have been examined with DFT (B3PW91) calculations. For a given arene, the rhenium moiety is shown to exhibit the following order of thermodynamic preference for coordination: HCCH site > HCCF site > FCCF site. Binding energies to the different arenes do not follow a clear trend and span ca. 20 kJ mol−1. The Re–C bond energies in CpRe(CO)(H)(C6FnH5−n) span 55 kJ mol−1. Calculated structural parameters agree with the crystal structure of coordination of C6H6 and C6F6. Likewise the binding energy of C6H6 is in good agreement with experimental data. The calculated free energy difference between CpRe(CO)2(η2-C6FnH6−n) and CpRe(CO)2(H)(C6FnH5−n) shows that preference for the hydrido–aryl complex is determined principally by the bond dissociation energy of the C–H bond of the free arene. The binding energy to the η2-arene appears to be only a secondary factor. Three families of complexes are apparent. If there is no F on the carbon ortho to the Re–C bond that is formed, the η2-arene complex is energetically preferred. If there is one F at the ortho position, the energies of the products are similar. In the case of two ortho F substituents, the product of oxidative addition is significantly favoured. In agreement with the calculations, experimental evidence shows that benzene only coordinates to Cp*Re(CO)2, 1,4-C6F2H4 gives a mixture of products and 1,3-C6F2H4 gives only the hydrido–aryl complex. The arene with the stronger C–H bond is the one which gives more oxidative addition product because the Re–C bond energy increases with F substitution (and in particular with ortho F) more than twice as fast as the C–H bond dissociation energy. The reaction path for the overall transformation has been determined. The σ C–H complex is identified as an intermediate on the pathway for the oxidative addition. The initial product of oxidative addition is the cis hydrido–aryl isomer which subsequently isomerizes to the trans isomer. The rate determining step has been found to be the cis–trans isomerisation process and not the oxidation addition step. The cis–trans isomerisation proceeds via an unconventional concerted motion of H and the two COs. The variation of the Re–C bond energy is the dominant factor in determining the changes in the energy barrier between the different fluoroarenes, resulting in strong correlation between the thermodynamics and kinetics of reaction. The activation barriers are therefore also grouped in three families (0 F ortho, 1 F ortho, 2 F ortho).

Molecular orbital calculations of binuclear systems of Fe, Co and Ni derivatives of pentalene, s-indacene and as-indacene

Abstract Extended Huckel calculations on a whole family of dinuclear complexes of pentalene, s-indacene and as-indacene allow a general rationalization of the structural and physical features of these compounds, mainly based on their electron count.

Synthesis, reactivity and molecular structure of phosphino tetramethyl cyclopentadienyl complex (η5: η1-C5Me4CH2PPh2)Re(CO)2

The fulvene complex (eta(6)-C(5)Me(4)CH(2))Re(C(6)F(5))(CO)(2) reacts at the exocyclic methylene carbon with potassium diphenylphosphide to yield the anionic species [(eta(5)-C(5)Me(4)CH(2)PPh(2))Re(C(6)F(5))(CO)(2)](-) (). Protonation of with HCl at 0 degrees C produces the hydride complex trans-(eta(5)-C(5)Me(4)CH(2)PPh(2))Re(C(6)F(5))(H)(CO)(2) (). Thermolysis of a hexanes solution of , under nitrogen atmosphere, produces the chelated complex (eta(5):eta(1)-C(5)Me(4)CH(2)PPh(2))Re(CO)(2) () in good yield. The thermolysis under a CO atmosphere affords a mixture of the complexes (eta(5):eta(1)-C(5)Me(4)CH(2)PPh(2))Re(CO)(2) () and (eta(5)-C(5)Me(4)CH(2)PPh(2))Re(CO)(3) (). The reaction of with two electron donor ligands yields (eta(5)-C(5)Me(4)CH(2)PPh(2))Re(CO)(2)(L) (, L = CO; , L = PMe(3); , L = (t)BuNC). Complex also reacts with I(2), HBF(4) and MeOTf to yield the cationic compounds trans-[(eta(5):eta(1)-C(5)Me(4)CH(2)PPh(2))Re(R)(CO)(2)](+) (, R = I; , R = H; , R = Me). Upon treatment with chloroform, the hydride complex converts to the corresponding chloro derivative . The trans stereochemistry for complexes have been assigned on basis of nu(CO) IR intensities and (13)C-NMR chemical shifts. The reaction of the cationic complexes (, ) with KI and Me(3)NO.2H(2)O yields the neutral species cis-(eta(5):eta(1)-C(5)Me(4)CH(2)PPh(2))Re(I)(R)(CO) (, R = I, , R = Me). The molecular structure of and have been determined by X-ray crystallography.

Selectivity in C–Cl bond activation of dichloroarenes by photogenerated Cp*Re(CO)2: combined experimental and DFT studies

The photochemical reaction of the d6 Re(I) complex Cp*Re(CO)3 with several substituted dichloroarenes (1-R-2,4-dichlorobenzene; R = Me, OMe, CF3 and F) yields the insertion products trans-Cp*Re(CO)2(C6H3ClR)Cl. The C–Cl bond activation of 2,4-dichloroanisole and 2,4-dichloro-1-fluorobenzene occurs at position 2 (ortho to the methoxy and fluoro substituents, respectively), whereas for 2,4-dichlorotoluene and 2,4-dichloro-1-trifluoromethylbenzene the C–Cl bond in position 4 (para to the Me and CF3 groups, respectively) is cleaved. The products have been characterized by elemental analyses and spectroscopic techniques, and by X-ray crystallography for the complexes trans-Cp*Re(CO)2(5-chloro-2-methoxyphenyl)Cl and trans-Cp*Re(CO)2(3-chloro-4-methylphenyl)Cl. DFT(B3PW91) calculations have been carried out to explain the selectivity observed in the isolated insertion products. It is shown that the Re–aryl bond dissociation energy is stronger in the observed isomer. This is analyzed as originating from a combination of electronic and steric factors.

Reactions of the tetramethylfulvene ligand coordinated to rhenium with hydrohalic acids and halogens: synthesis of dicarbonyl complexes with a ‘four-legged piano-stool’ structure containing mixed-halide ligands

Abstract The new tetramethylfulvene complexes of rhenium (η 6 -C 5 Me 4 CH 2 )Re(CO) 2 X, (X=Cl, Br, I) have been synthesized from (η 5 -C 5 Me 5 )Re(CO) 2 X 2 by a two step procedure and fully characterized by elemental analysis, IR and NMR spectroscopies. Reaction of (η 6 -C 5 Me 4 CH 2 )Re(CO) 2 X (X=Br, I) with HX′ regenerated the (η 5 -C 5 Me 5 ) ligand with the formation of the mixed-halide complexes cis -(η 5 -C 5 Me 5 )Re(CO) 2 XX′ (X=I, X′=Br; X=I, X′=Cl; X=Br, X′=Cl), whereas, the reaction with halogens (X′ 2 ) gave analogous complexes containing a halide substituted tetramethylcyclopentadienyl ligand, cis -(η 5 -C 5 Me 4 CH 2 X′)Re(CO) 2 XX′ (X=Br, X′=I; X=I, X′=Br). In both types of complexes the cis stereochemistry have been assigned on the basis of ν (CO) IR intensities and δ (CO) 13 C-NMR. 4

SYNTHESES AND REACTIONS OF THE COMPLEXES (η5-C5Me5)Re(CO)2(C6CL5–nHn)Cl (n = 2,3): COMPOUNDS DERIVED FROM INITIAL C—CI ACTIVATION

Abstract The UV irradiation of (η5-C5Me5)Re(CO)3 in the presence of 1,2,4,5-C6Cl4H2 and 1,3,5-C6Cl3H3 (λ = 350 nm, hexane solution) effected intramolecular C—Cl activation, generating the complexes trans-(η5-C5Me5)Re(CO)2(2,4,5-C6Cl5-nHn)Cl, ((1), n = 2; (2), n = 3), respectively. Complex (1) dissolved in polar organic solvents produces, an equilibrium mixture with its cis isomer. The reaction of (1) with AgBF4, in acetonitrile, led to formation of the cationic complex [cis-(η5-C5Me5)Re(CO)2(2,4,5-C6Cl3H2)(MeCN)]+. The tetramethylfulvene complex (η6-C5Me4CH2)Re(CO)2(2,4,5-C6Cl3H2) (3) was obtained by reacting the cationic complex with the fluorinating agent Et3N′3HF.

Direct and high yield syntheses of Re2(CO)10 and Re(CO)5Cl by sodium reduction of K2ReCl6 under CO

Abstract A convenient procedure for the synthesis of the rhenium carbonyls Re 2 (CO) 10 and Re(CO) 5 Cl is reported. Sodium reduction of the easily available K 2 ReCl 6 , under CO pressure (2400 psi, 280°C (external temperature), THF as solvent) affords Re 2 (CO) 10 and Re(CO) 5 Cl in 81% and 86% isolated yield, respectively. Depending on the hexachlororhenate:Na ratio, either carbonyl derivative can be obtained almost exclusively.

REACTION OF TETRAMENTHYLFULVENE RHENIUM COMPLEXES (η6-C5Me4CH 2)Re(CO)2R (R = I, C6F5) WITH ALKYL PHOSPHINES AND TRIMETHYLPHOSPHITE: X-RAY STRUCTURE OF [(η5-C5Me4CH 2-(PMe3))Re(CO)2(PMe3)]+ I-

The fulvene complex (η6-C5Me4CH2 )Re(CO)2(C6F5) 1a reacts with alkyl phosphines to yield the zwitterionic species (η5-C5Me4CH2 PR3)Re(CO)2(C6F 5) 2 (R = Me, Et, iPr). Reaction of the analogous iodo complex (η6-C5Me4CH2 )Re(CO)2I, 1b, with PMe3 and PEt3 affords the cationic species [(η5-C5Me4CH2 (PR3))Re(CO)2(PR3)] + I- 3 (R = Me, Et). However, reaction of 1b with Pi Pr3 yields the zwitterion (η5-C5Me4CH2 PiPr3)Re(CO)2 (I) 4. Trimethyl phosphite reacts with both 1a and 1b to afford the phosphonate complexes (η5-C5Me4CH2 P(O)(OMe)2)Re(CO)2(P(OMe) 3) 5a and trans-(η5C5Me4 CH2P(O)(OMe)2)Re(CO)2 (C6F5)(Me) 5b respectively. The complex [(η5-C5Me4CH2 (PMe3))Re(CO)2(PMe3 )]+ I- 3a has been characterized by X-ray structural analysis

η²-COORDINATION OF CHLOROBENZENES TO RHENIUM FRAGMENT Cp*Re(CO)2: CHEMICAL AND PHOTOCHEMICAL SYNTHESES OF Cp*Re(CO)2(η²-C6H6-nCl n)

ABSTRACT The complexes Cp*Re(CO) 2 (h 2 -C 6 H 6-n Cl n ), n = 4, (5,6-h-1,2,3,4-C 6 H 2 Cl 4 ) 2a ; n = 3, (5,6-h 2 -1,2,4-C 6 H 3 Cl 3 ) 2b ; n = 2, (2,3-h 2 -1,4-C 6 H 4 Cl 2 ) 2c and (4,5-h 2 -1,3-C 6 H 4 Cl 2 ) 2d , have been conveniently prepared by two alternative procedures: Directly, by the photochemical reaction of Cp*Re(CO) 2 (N 2 ) in neat or saturated hexane solution of the corresponding partially chlorinated benzene or stepwise, by the reaction of the appropriate trans-Cp*Re(CO) 2 (Ar Cl )X, X = Cl, Br ( 1a-d ) with LiBHEt 3 followed by protonation with HCl to form the hydrido complexes trans-Cp*Re(CO) 2 (Ar Cl )H which resulted thermally unstable in solution and convert to h 2 -coordination complexes 2a-d . Due to their low stability as solids and in solution, the new complexes were only characterized by IR and 1 H and 13 C NMR spectroscopy. The 1 H NMR spectra of the two derivatives containing dichlorobenzene ( 2c and 2d ) indicate that a rapid exchange occurs between the hydrogen atoms on the coordinated carbons and those on the non-coordinated carbons.e-mail: fernando.godoy@usach.cl

Bond energy M–C/H–C correlations: dual theoretical and experimental approach to the sensitivity of M–C bond strength to substituents

DFT methods are used to quantify the relationship between M-C and H-C bond energies; for MLn = Re(eta5-C5H5)(CO)2H and fluorinated aryl ligands, theoretical and experimental investigations of ortho-fluorine substitution indicate a much larger increase in the M-C than in the H-C bond energy, so stabilising C-H activation products.