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We report the synthesis and characterization of a μ-hydroxo NiRu complex as a model for the active site of (Ni–SIr)I of [NiFe]hydrogenase. This is the first example of the (Ni–SIr)I model with a bridging hydroxo ligand between dimetal centers and an available coordination site on Ni center cis to the bridging hydroxo ligand. We have determined the structure of the (Ni–SIr)I model complex by X-ray analysis and reported reversible switching between the catalytically inactive (Ni–SIr)I and a catalytically active (Ni–SIr)II models.

A new concept for a light-gated transition metal catalyst is presented based on a photo-active moiety in the outer ligand sphere of the complex which on irradiation reacts irreversibly with some part of the inner ligand sphere releasing a free coordination site. The principle is exemplified on a platinum complex for the hydrosilylation. It is proven that the catalytic properties of the complex and the properties of the photo-gate can be fine-tuned on the chemical problem independently of each other.

Heterometallic clusters containing a perpendicularly coordinated alkyne ligand, (Cp*Ru) 2 (Cp*Ir)(μ 3 –η 2 :η 2 (⊥)-PhCCR)(μ-H) 2 ( 6a , R = Me; 6b , R = Ph), were prepared by the reaction of a trinuclear heterobimetallic tetrahydrido complex of ruthenium and iridium, (Cp*Ru) 2 (Cp*Ir)(μ-H) 3 (μ 3 -H) ( 2 ), with internal alkyne. X-ray diffraction studies clearly showed that the alkyne ligand was preferentially attached to the Ru–Ru bond in a perpendicular manner rather than to the Ru–Ir bond. Although no detectable changes were observed in a VT-NMR study on 6a , VT-NMR studies on 6b implied that the alkyne ligand underwent a switchback motion at the heterometallic site. The presence of the minor isomer 8b , in which the alkyne ligand was attached to the Ru–Ir bond, was also proposed by the density functional theory (DFT) calculations. The energy difference between 6b and 8b is estimated at 4.1 kcal mol −1 . These results suggest that the coordination site of the alkyne ligand was determined thermodynamically.

The stepwise displacement of pip (= piperidine) from cis-(pip)2W(CO)4 by 2-allylphenyldiphenylphosphine (adpp) affords cis-(η3-adpp)W(CO)4 (4) when the cis-(pip)(η1-adpp)W(CO)4 intermediate (2; adpp is P-bonded) is isolated and purified; directly, this reaction affords a 85/15 ratio of 1 to cis-(η3-pdpp)W(CO)4 (3; pdpp = 2-propenylphenyldiphenylphosphine). In contrast, it had been reported that displacement of norbornadiene (= NBD) from (η4-NBD)M(CO)4 by adpp affords primarily 3. It is concluded that olefin bond-migration takes place in a η3-allylmetal hydride intermediate produced from a [(η2-adpp)W(CO)4] precursor in which adpp is coordinated cis to a vacant coordination site through the olefinic linkage.

Using metal carbonyl fragments as templates, the directed, bridging alkylation of ligating dithiolates yields macrocyclic polythioethers. Treatment of cis -[Fe(CO) 2 -(S 2 C 6 H 4 ) 2 ] 2− ( 1 ) with S(C 2 H 4 Br) 2 , in THF at room temperature, gives [Fe(CO)-(dpttd)] ( 2 ) (dpttd 2− = 2,3,11,12-dibenzo-1,4,7,10,13-pentathiatridecane(2−)), which is alkylated by yet another S(C 2 H 4 Br) 2 under reflux to give dibenzo-18-crown-S6 ( 3 ) in 68% yield after hydrolysis and workup. Alkylation of [Fe(CO) 2 dttd] (dttd 2 = 2,3,8,9-dibenzo-1,4,7,10-tetrathiadecane(2−)) by S(C 2 H 4 Br) 2 in THF under reflux gives analogously dibenzo-15-crown-S5 ( 4 ) in 20% yield. 4 is also obtained by alkylation of 2 with 1,2-C 2 H 4 Br 2 , but in lower yield. Since each C 6 H 4 S 2 2− ligand in 1 is alkylated only once at room temperature the Fe(CO) 2 fragment acts as a protecting group for one thiolate function and permits the monoalkylation of o -benzenedithiol, a reaction which is not possible by conventional methods; with PhCH 2 Br and CH 3 Br the corresponding alkylthiobenzenethiols were obtained. An X-ray diffraction study of 3 shows it to have an unprecedented conformation viz. in the centrosymmetric molecule all six sulfur atoms and the C 2 (ethane) bridges form a plane (maximum deviation ± 8 pm) on which the benzo units stand nearly upright (83°). All sulfur atoms are exo and four of the twelve CS bonds show anti configuration. A comparison of the structures of 3 and the analogous oxo compound dibenzo-18-crown-6 are described.

The coordination site of Cr(CO)3 in diarylimines derived from aromatic aldehydes or ketones and aromatic amines has been studied. The results show that electron density is not a unique determining factor. It is suggested that consideration of the three ligand π levels (energy, symmetry, representativity) can account for the results.

Upon carbonylation of pseudotetrahedral di-η5 -cyclopentadienylzirconium (IV) complexes under kinetic control the η2-acyl compounds (IV) with the acyl-oxygen bound to a lateral coordination site are formed. The isomers IV are separated from the thermodynamically favored isomers V by a substantial activation barrier. The corresponding η2-acetyl complexes show the lowest barrier thus far observed for this type of isomerisation (VII → VIII: ΔG≠−123°C 11.4 kcal mol−1).

8-Methyl- and 8-ethyl-quinolines give cyclopalladation products with palladium acetate by CH bond cleavage at the 8-substituent, but 8-isopropylquinoline does not. The influence on cyclometallation of introducing 2-substituents (Me, Br, CHO, CHNMe, CH2OH, CO2H) in these quinolines is described. The first three substituents totally prevent cyclopalladation whereas metallation at the 8-substituent proceeds smoothly when the 2-substituent is CHNMe, CH2OH or CO2H. The products are characterised spectroscopically and there is a discussion of the dynamic 1H NMR behaviour of the cis and trans isomers of [Pd(OAc)(CH2C9H6N]2 formed from 8-methylquinoline. Evidence is presented that the cyclopalladation reaction takes place for a three-coordinate palladium(II) intermediate with the reacting hydrocarbon group entering the vacated fourth coordination site.

A method for the synthesis of stereospecifically, equatorially labelled cis -M(CO) 4 ( 13 CO)(amine) derivatives where M = Cr, Mo, and W has been developed involves 13 CO substitution into the vacant coordination site created by the facile dissociation of an amine ligand from cis -M(CO) 4 (amine) 2 derivatives. The mechanistic implications of this extremely stereoselective reaction are discussed.

In the reaction with phenylacetylene leading to [(PPh 3 ) 2 (CO)IrCl (HNNC 6 H 4 R- p )(CCPh)] (BF 4 ) (R  NO 2 , CN, COCH 3 ), the vacant coordination site in [(PPh 3 ) 2 (CO)IrCl(N 2 C 6 H 4 R- p )] (BF 4 ) plays a key role in the activation of the acetylenic CH bond. ca]To whom correspondence should be addressed.