Catalytic cross-coupling of diazo compounds with coinage metal-based catalysts: an experimental and theoretical study

Abstract

We examined the ability of Tp x M (Tp x = hydrotris(pyrazolyl)borate ligand; M = Cu and Ag) and IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene; M = Cu, Ag, Au) complexes as catalyst precursors for the cross-coupling of diazo compounds. Experimental data showed that the metal centre can be tuned with the appropriate selection of the ligand to yield either the homo-or hetero-coupling (cross-coupling) products. A computational study of the reaction mechanism allowed the rationalization of the experimental reactivity patterns, and the identification of the key reaction step controlling the selectivity: the initial reaction between the metallocarbene intermediate and one of the diazo compounds.

Copper–Carbene Intermediates in the Copper‐Catalyzed Functionalization of OH Bonds

“…When a CH 2 Cl 2 solution of 1 and 3 equiv of Pheda prepared at −30 °C was allowed to reach room temperature, the color changed from reddish to dark brown and then to dark orange. NMR studies of the final mixture showed a combination of products including 1) (Ph)(OH)CH(CO 2 Et) resulting from the insertion of the C(Ph)(CO 2 Et) unit into the OH bond of adventitious water, 2) the olefins resulting from carbene coupling, E ‐ and Z ‐(Ph)(CO 2 Et)CC(Ph)(CO 2 Et), and 3) the azine EtO 2 C(Ph)CNNC(Ph)CO 2 Et (Scheme ) 13. Monitoring the reaction by using 13 C{ 1 H} NMR spectroscopy in CD 2 Cl 2 showed that at −40 °C only the resonances assigned to the diazo adduct 2 a ( 13 C‐enriched) were observed.…”

“…FTIR spectra were recorded on aNicolet IR200 FTIR spectrometer. 1 Ha nd 13 CNMR shifts were measured relative to deuterated solvents peaks but are reported relative to tetramethylsilane. 19 FNMR chemical shifts are reported relative to external CFCl 3 .E lemental analyses were performed on aP erkinElmer Series II CHNS/O Analyzer 2400.…”

“…NMR studies of the final mixture showedacombination of products including 1) (Ph)(OH)CH(CO 2 Et) resulting from the insertion of the C(Ph)(CO 2 Et) unit into the OÀHb ond of adventitious water,2 )the olefins resulting from carbenec oupling, Eand Z-(Ph)(CO 2 Et)C=C(Ph)(CO 2 Et), and 3) the azine EtO 2 C(Ph)C= NÀN=C(Ph)CO 2 Et (Scheme 5). [13] Monitoring the reactionb y using 13 C{ 1 H} NMR spectroscopy in CD 2 Cl 2 showedt hat at À40 8Co nly the resonances assignedt ot he diazo adduct 2a ( 13 C-enriched) were observed. The temperature was then progressivelyi ncreased and, at + 10 8C, an ew resonance raised at d = 248.5 ppm, whichw as assigned to the carbene carbon of the complex [Tp Ms Cu= 13 C(Ph)(CO 2 Et)] (3a)o nt he basis of the previously described copper carbenes by the groups of Hofmann (Scheme 2a, d=229.9 ppm), [10a] Barluenga (Scheme 2b, d=276.5 ppm), [10b] and Warren (Scheme 2c, d=253.1 ppm).…”

“…Following the same procedure, the three other Tp x Cu complexes (see Scheme 4) behaved similarly leading to the formation of the corresponding copper-carbene complexes[ Tp x Cu= 13 C(Ph)(CO 2 Et)] (Tp x = Tp Me2 , 3b;T p i Pr2 , 3c;F 12 -Tp 4Bo, 3Ph , 3d). Figure 2s hows the downfield region of the 13 CNMR spectra in which the carbenic carbon resonates ( 13 C-labelled Pheda was employed in all cases). The chemical shift increased in the order Tp iPr2 < Tp Me2 < Tp Ms < F 12 -Tp 4Bo, 3Ph .I nterestingly,w eh ave found that there is ag ood linear correlation between the values of n(CO) of the [Tp x Cu(CO)] complexes and the chemical shift of the carbenic carbon (Table 1and Figure 3).…”

Iron and Manganese Catalysts for the Selective Functionalization of Arene C(sp2)−H Bonds by Carbene Insertion

“…One of them is the so-called Buchner reaction (Scheme 1C), [5,6] that occurs by formal addition of the carbene unit to the arene C = Cb ond yielding an orcar-adiene which spontaneously opens producing the cycloheptatriene.The opposite transformation, i.e.the retro-Buchner or Echavarren reaction has been described. [8] Thef ormal insertion [9] of ac arbene group from ad iazo compound in the CÀHb ond of benzene was independently reported by the groups of Schechter [10] and Livant, [11] using Rh 2 (OAc) 4 as the catalyst, at refluxing temperature,and with the diazo compounds shown in Scheme 2. [8] Thef ormal insertion [9] of ac arbene group from ad iazo compound in the CÀHb ond of benzene was independently reported by the groups of Schechter [10] and Livant, [11] using Rh 2 (OAc) 4 as the catalyst, at refluxing temperature,and with the diazo compounds shown in Scheme 2.…”