Other Transition Metal Catalysts

There are three areas of activity in the field of arenediazonium salts in interaction with metals and transition elements which have some similarities to metals. First is the use of copper in the reactions of Sandmeyer (1884), Pschorr (1896), Gomberg-Bachmann (1924), and Meerwein (1939). Other transition metal catalysts (Ti and Pd) have been used for such reactions since the 1970s (see Secs. 10.8 and 10.9). Up to now only one intermediate has been directly identified, the aryldiazenido palladium complex (ArN2Pd(PPh3)3]+BF4 (Yamashita et al., 1980 see Sec. 10.9, Scheme 10-64). 

The addition of allcenes to alkenes can also be accomplished by bases as well as by the use of catalyst systems consisting of nickel complexes and alkylaluminum compounds (known as Ziegler catalysts), rhodium catalysts, and other transition metal catalysts, including iron. These and similar catalysts also catalyze the 1,4 addition of alkenes to conjugated dienes, for example. 

A synthetically useful example uses 2-[(trimethylsilyl)methyl]-2-propen-1-yl acetate (95), which is commercially available, and a palladium or other transition metal catalyst to generate 96 or 97, which adds to double bonds, to give, in... 

In recent years, much attention has been focused on rhodium-mediated carbenoid reactions. One goal has been to understand how the rhodium ligands control reactivity and selectivity, especially in cases in which both addition and insertion reactions are possible. These catalysts contain Rh—Rh bonds but function by mechanisms similar to other transition metal catalysts. 

Another remarkable property of iodorhodium(III) porphyrins is their ability to decompose excess diazo compound, thereby initiating carbene transfer reactions 398). This observation led to the use of iodorhodium(III) me.vo-tetraarylporphyrins as cyclopropanation catalysts with enhanced syn anti selectivity (see Sect. 2.2.3) s7, i°o) as wep as catalysts for carbenoid insertion into aliphatic C—H bonds, whereby an unusually high affinity for primary C—H bonds was achieved (see Sect. 6.1)287). These selectivities, unapproached by any other transition metal catalyst,... 

B. Other Transition Metal Catalysts with Chiral Phosphines. 356... 

In contrast to the palladium-catalyzed reactions, little attention has been paid to other transition-metal catalysts. Recently some efficient reactions using copper(i or 11), gold(m), platinum(n), and tungsten(O) have been developed for the synthesis of nitrogen-heterocycles. The copper-catalyzed cyclizations of 2-alkynylaniline derivatives into... 

Matsuda and co-workers described the first intermolecular rhodium-catalyzed [4-1-2] reaction in 1987 [5]. Consistently with the other transition metal catalysts that had been developed for similar systems, the rhodium-catalyzed version was also limited to... 

Other transition metal catalyst RuTp(L)(LOCl (L, L = P, N, O donors) Et2NC02RuH(C0)(PCy3)2 (PhC )2Ru(CO)(PCy3)2 [(Cp )RuC12]2... 

Nickel and other transition metal catalysts, when modified with a chiral compound such as (R,R)-tartaric acid 5S), become enantioselective. All attempts to modify solid surfaces with optically active substances have so far resulted in catalysts of only low stereoselectivity. This is due to the fact that too many active centers of different structures are present on the surface of the catalysts. Consequently, in asymmetric hydrogenations the technique of homogeneous catalysis is superior to heterogeneous catalysis56). However, some carbonyl compounds have been hydrogenated in the presence of tartaric-acid-supported nickel catalysts in up to 92% optical purity55 . 

Iron Complexes as Ligands for Other Transition Metal Catalysts... 

Catalytic hydroboration is a new methodology of great synthetic potential. The reaction is usually carried out with catecholborane in the presence of rhodium, palladium, iridium and ruthenium compounds.2 In contrast to olefins, very little is known on catalytic hydroboration of conjugated dienes and enynes. Our earlier studies on the uncatalyzed monohydroboration of conjugated dienes,6 reports on the hydroboration of 1-decene with catecholborane catalyzed by lanthanide iodides,7 and monohydroboration of 1,3-enynes in the presence of palladium compounds,8 prompted us to search for other transition metal catalysts for monohydroboration of conjugated dienes and enynes 9 10... 

Except for the metallic impurities present on the walls of poorly washed glassware, no other transition metal catalyst may be assumed to be present in this experiment. Consequently, the transfer of the dimethylamino group from the ortho amide II to I must be taking place under less energy demanding conditions, where protic acid catalysis suffices to activate the triple carbon to carbon bond. ... 

Over Ni at 500-700°C, principally CH forms". Other transition-metal catalysts result in higher yields of C>, products. Ethylene glycol is produced effectively from CO and Hj using homogeneous Rh catalysts ... 

HYDROGENOLYSIS WITH PALLADIUM AND ITS DERIVATIVES AND WITH OTHER TRANSITION METAL CATALYSTS... 

Copper-catalyzed substitution of allylic halides (and related cases) with Grignard reagents has been extensively studied (see Section III). To a lesser extent the use of other transition metal catalyst, such as Ni, Fe, Ti. Mn, Cr, remains anecdotally studied. 

Of course, the catalytic cyclooligomerization of BD is not limited to nickel as template. Other transition metal catalysts and reaction products are listed in Table 5 [17-25] and Table 6 [26-30]. 

The air-stable rhodium carbonyl cluster Rhg(CO),g displays a similarly high catalytic efficiency as does RhjlOAc) Table 6 gives some examples. Comparisons of Rhg(CO)jg with RhjCOAc), PdCl 2 PhCN and CuCl P(O-Z-Pr)j are given in Table 7, They show once more that the rhodium catalysts are superior to other transition-metal catalysts. Rh COAc) gives consistently the highest yields, whereas the activity of Rhg(CO)jg depends on the olefin used. Because of its insolubility in olefins, it is probably the extent to which an active, homogeneous catalyst is formed, which imposes certain limits on the versatility of Rhg(CO)jg. Results comparable to those in Table 7 were also obtained with monosubstituted 1,3-dienes... 

These selectivities, unapproached by any other transition metal catalyst. 

The original material (subsequently called URPAC) is accessible in various morphologies with a large number of Ziegler-Natta type and other transition metal catalysts. It has been studied in detail with spectroscopic and other physicochemical methods. Quantum theoretical model calculations have provided insights into the energetics of conjugated double bond systems. 

---