With the advent of Skell's carbon vapor reactor[lJ, interest in the use of high temperature species as reagents for carrying out syntheses has increased greatly, as recently pointed out by Timms' excellent reviewf2'. The most advantageous use of this technique has been in organotransition metal chemistry. Thus, high temperature transition metal atoms are condensed at low temperature (usually -196Β°C) simultaneously with vapors of organic substrates. The high temperature atoms are formed by vaporizing metals from resistively heated crucibles, by arcingL3] or by laser heatingL4]. These atoms have a high chemical potential, and react at low temperature with the organic substrates to form many unusual compounds. Thus, the method can be termed the "metal atom technique" or "freeze-fry chemistry."
Our main interest has been in using the metal atom technique as a way of making some rather unusual and interesting organometallic species. To do this we have assembled a simple metal atom reactor (see Section 6), in which all of the first row transition metals (excepting scandium) as well as Pd, Pt, Zn, and Ag have been studied.
We have been most interested in the metals V(123), Cr(95), Ni(103), Pd(89), and Pt(135). Shown in parentheses are the heats of formation (kcal/mol) of these metals which indicates the amount of energy needed for vaporization, and thus gives a rough idea of the high reactivity of these species.
Three main areas have interested us: (1) the synthesis of polyhalogenated n-complexes of the transition metals; (2) oxidative insertion of metal atoms into carbon-halogen, carboncarbon, and carbon-oxygen bonds; and (3) preparation of clean, finely-divided active metals.
2. Polyhalogenated n-Complexes
Normal solution techniques have not been successful in preparations of most polyhalogenated n-complexes of the transition metals. Thus, polyhalogenated bis(arene)-complexes of V and Cr, and n-ally1 complexes of Co, Ni, Pd, Pt have not been prepared by classical methods. There are several possible reasons for the failure of such procedures, but probably the most important reasons are the presence in solution of nucleophiles (e. g. fluoride ions) and/or solvent that can cause facile rearrangements, decompositions, or competitions for open sites on the metal. The metal atom technique avoids these problems. In the case of bis(arene) complexes, the metal atom technique has been quite useful, as has been previously