Transition metals, bonds with arsenic

B5.1 Structural chemistry of transition metal complexes with arsenic-arsenic bonds... 

L. Preparation of Compounds with Arsenic(III)-Transition Metal Bonds. 848... 

The arsenic-transition metal bond has been formed by reaction of arsenic hydrides with Co and Ir compounds (equations 243 , 244 and 245 ). 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

The synthesis of stable complexes with transition metal-phosphorus triple bonds is of fundamental importance and opens a novel chapter of a special field of coordination chemistry. The synthesis of analogous complexes with ligands of the heavier homologues like arsenic has partially been carried out [6], while for antimony and bismuth, the elusive M=Sb and M=Bi systems have now moved within reach. Moreover, the experimental and theoretical... 

The As—N bond is labile and this has been widely exploited in synthetic arsenic chemistry. Some idea of the versatility168 can be seen from Schemes 1 and 2. Refluxing secondary amines with tris(dimethylamino)arsine effects transamination (equation 6). These tris(dialkyl-amino)arsines undergo the general reactions in Scheme 1, enabling ready access to a wide variety of compounds, many of them finding use as ligands in transition metal complexes (see Chapter 14 of this work). 

The complex of tartaric acid and antimony (emetic) was described three centuries ago. Nevertheless, the structure of this compound has been elucidated these last fifteen years by X-ray diffraction ( 1 ). In fact, emetic presents a binuclear cyclic structure. Many authors mentioned similar complex with transition metals (vanadium (2), chromium (3)) or metalloids (arsenic (4), bismuth (5)). Emetic with phosphorus was not mentioned. Nevertheless, tartaric acid or alkyl tartrates has been utilized in phosphorus chemistry tartaric acid reacts with trialkyl phosphites giving heterocyclic phosphites (6). Starting from alkyl tartrates, we prepared spirophosphoranes with a P-H bond and sixco-ordinated compounds (7). With unprotected tartaric acid, many possibilities appear condensation as a diol, as a di(oc-hydro-xyacid), or even as a 8-hydroxyacid. 

Another manifestation of covalent bonding relates to the sulphide mineralogy of the transition elements. Although earlier chapters have stressed properties of transition metal ions in oxides and silicates, an important feature of these elements is the frequency of their geochemical association with B-sub-group non-metal and metalloid elements such as sulphur, selenium, tellurium, phophorus, arsenic and antimony. The chalcophilic properties of iron, cobalt, nickel and copper in the crust are well known and are important eco-... 

The transition-metal chemistry and nature of the complexes formed with As-As bonded compounds has been reviewed. The reader is referred to this comprehensive review for an overview of the nature of complexes that contain chains of coordinated R-As units, heterocyclic As-chalcogen rings, and unsubstituted arsenic atoms and for references to the primary literature. The limited transition-metal chemistry of the phosphaarsenes and diarsenes is also reviewed. ... 

The intermediate of the irreversible isomerization can be isolated. The EMc2 unit is <7 bonded in the educt it is a centre of basic activity, shoeing tendency for reactions with electrophiles. Thus the electron-rich state of the atoms of group 15 elements leads to irreversible isomerization with shifting of one methyl group from the PR3 ligand to arsenic or antimony, respectively. The donor capacity of the transition metal is enlarging this ability. 

A cationic Sb(III) ligand is part of the tungsten complex [Cp(CO)2(Me3P)WSb(Me)-(Cl)Bu ]I, which was prepared from tr ns-Cp(CO)2(MeP)WSb(Cl)Bu and Mel in Et20 . The first transition metal complexes containing a metal-arsenic double bond were synthesized in 1983 . Transition metal substituted arsines of the type Cp(CO)3M—AsBu 2 (M = Mo, W) show increased Lewis basicity compared with triorganoarsines R3AS. From the above-mentioned complex one carbonyl is cleavable already at 60 °C (equation 35). 

Diarsine and distibine ligands. The n bond in ligands of the type RE = ER (E = P, As, Sb) is naturally very reactive but may be protected by a side-on coordination to a transition metal atom. The ligand is -bound with a bond order of approximately 1.5. Therefore, arsenic and antimony coordinate either via the lone-pair of electrons as a... 

The cycloarsines (PhAsj and (MeAs)j also behave as sources of the isolobal arsenic analogue of the allyl ligand, i.e. RAsAsAsR, on reaction with [Cp M 0)2] 2 (for M = Mo or W) to give products with the stoichiometry Cp M(CO)2 (RAsAsAsR) . Each arsenic atom is bonded to the transition metal and the As—As distances are equal (2.361 A), representing a bond order of 1.5 as expected for an allylic analogue. 

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