The introduction of heavy atoms into protein crystals is sometimes rendered difficult and tedious because of the poor specificity of the available reagents for particular target residues. On the other hand, transition organometallic chemistry offers an almost untouched field for this purpose. In particular, Fischer-type metallocarbene complexes of the general formula (CO) 5 W¼C(OR 1 )R 2 may be attractive reagents because they contain the heavy element tungsten and specifically target amino groups to form stable, covalent aminocarbene adducts. With a small protein such as hen egg white lysozyme (HEWL) with a limited number of potential binding sites, it was possible to form protein-aminocarbene conjugates that have an average of one aminocarbene moiety per protein molecule. RP-HPLC combined with matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MS analysis of the conjugates revealed that they were mixtures of the native protein, monoaminocarbenes and diaminocarbenes. Tryptic proteolysis experiments performed on the protein conjugates combined with MALDI-TOF-MS analysis of the aminocarbenic peptides allowed us to determine that lysines 13, 33, 97 and 116 were involved in the reaction of HEWL with (CO) 5 W¼C(OMe)Me.Keywords: Fischer-type metallocarbene complexes; lysine residues; lysozyme; MALDI-TOF-MS.The preparation of heavy metal derivatives, i.e. the incorporation of heavy atoms into protein crystals, is the traditional approach to determine diffraction phases in the course of protein 3D structure resolution by X-ray crystallography [1]. This step is essential for the construction of an electrondensity map and therefore a 3D model of the protein. Suitable reagents should make it possible to incorporate the heavy element at a limited number of binding sites with a high occupancy factor and not disturb the crystal packing or protein folding (isomorphous replacement). Unfortunately, selection of reagents is often a trial-and-error process because such reagents are not selective of particular binding sites [2]. Moreover, mercury compounds are known to be toxic to handle.In the last few years, we have been designing new heavy metal reagents based on transition organometallic complexes. This particular class of metal complexes made it possible to design side-chain-selective reagents yielding covalent protein adducts [3 -5].More recently, we have shown that Fischer-type metallocarbene complexes of the general formula 1 react with a model protein, namely BSA, to form stable conjugates [6]. Indeed, these compounds display a highly electrophilic character at the carbene carbon atom and are therefore susceptible to nucleophilic substitution by amines (aminolysis) to yield very stable metalloaminocarbenes. (Scheme 1).This preliminary result suggested that these complexes may act as heavy atom reagents because (a) they target particular side chains and (b) they form covalent and stable adducts. We describe here the reaction of two Fischer-type carbene complexes, 1a and 1b, with the enzyme hen egg white...

The reaction of benzyne with 3,4-dimethylphosphole pentacarbonylmolybdenum complexes affords the corresponding 2,3-benzo-7-phosphanorbornadiene complexes through [4+2] cycloaddition. The condensation takes place on the less hindered side of the phosphole ring corresponding to the phosphorus substituent as shown by the X-ray crystal structure analysis of the phenyl derivative (2). The strain at the bridge of 2 (C−P−C angle ca. 80°) induces a variety of splitting reactions. Upon decomplexation by dppe at 110 °C in toluene, phenylphosphinidene is generated and recovered as phenylphosphine. Upon sulfurization under the same conditions, [PhPS2] is formed and trapped as a [4+2] adduct with 2,3-dimethylbutadiene. Potassium tert-butylate attacks the bridge in THF at −78 °C and, after methylation and hydrolytic workup, yields [Ph(Me)P(OH)Mo(CO)5].

The reaction of fluoride ion with 7‐phosphanorbornadiene P–W(CO)5 complexes yields fluorophosphido complexes which, in turn, can attack a second molecule of 7‐phosphanorbornadiene to give a fluorobiphosphine complex. The corresponding anion displays a huge P–P coupling. The structure of the anionic chromium analogue has been investigated by DFT calculations. The P–P bond is relatively short at 2.20 Å and displays a huge polarity suggesting an interesting chemistry. When the 7‐phosphanorbornadiene P‐substituent is 2‐chloroethyl, the attack of the fluoride ion is followed by a cyclization and a reductive dimerization leading to the first known biphosphirane complex.