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The catalytic activity of cyclobutadiene rhodium complexes was investigated in various transformations of alkynes. Complexes [Rh(C4Et4)Hal]n (at 1 mol% loading) were found to promote hydrosilylation of 1-octyne selectively giving 1-Z-, 1-E-, or 2-Et3Si-1-octene depending on the nature of the halide ligand and the presence of additional ligand PPh3. Complex [Rh(C4Et4)(p-xylene)]+ (1 mol%) also efficiently catalyzed the polymerization of phenylacetylene. At the same time, we found that various cyclobutadiene rhodium complexes do not catalyze the Diels–Alder reaction, alkyne hydration, and 1,4-addition of boronic acids to cyclohexanone. New complexes [Rh(C4Et4)(PPh3)2]BF4 and [Rh(C4Et4)(C10H8)]PF6 were also synthesized and their structures were established by X-ray diffraction. [ABSTRACT FROM AUTHOR]

The rhodium complex [(C5H2tBu2CH2tBu)RhCl2]2 with an asymmetric cyclopentadienyl ligand was prepared in 95% yield by the reaction of [(cod)RhCl]2 with tert-butylacetylene in the presence of AlCl3. A similar reaction in the presence of InBr3 gave the cationic fulvene complex [(C5H2tBu2 = CHtBu)Rh(cod)]InBr4 (70%), which can add alcohols ROH and produce more bulky catalysts [(C5H2tBu2CH(OR)tBu)RhCl2]2. The enantiomers of these planar-chiral complexes were separated by thin-layer chromatography in the presence of L-phenylglycinol. The complexes catalyze the reactions of arylhydroxamates with alkenes giving dihydroisoquinolones in excellent yields (80–90%), but with moderate enantioselectivity (typically 20–50% ee). [ABSTRACT FROM AUTHOR]

A new method for the synthesis of chiral diene rhodium catalysts is introduced. The readily available racemic tetrafluorobenzobarrelene complexes [(R2‐TFB)RhCl]2 were separated into two enantiomers via selective coordination of one of them with the auxiliary S‐salicyl‐oxazoline ligand. One of the resulting chiral complexes with an exceptionally bulky diene ligand [(R,R‐iPr2‐TFB)RhCl]2 was an efficient catalyst for the asymmetric insertion of diazoesters into B−H and Si−H bonds giving the functionalized organoboranes and silanes with high yields (79–97 %) and enantiomeric purity (87–98 % ee). The stereoselectivity of separation via auxiliary ligand and that of the catalytic reaction was predicted by DFT calculations. [ABSTRACT FROM AUTHOR]

On the basis of the 1,2,3,4‐tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C−C and C−N bonds. The halide compounds [(η5‐tetrahydrofluorenyl)RhX2]2 (2 a: X=Br; 2 b: X=I) were synthesized by treatment of the bis(ethylene) derivative (η5‐tetrahydrofluorenyl)Rh(C2H4)2 (1 a) with halogens. An analogous reaction of the cyclooctadiene complex (η5‐tetrahydrofluorenyl)Rh(cod) (1 b) with I2 is complicated by the side formation of [(cod)RhI]2. The reaction of 2 b with 2,2′‐bipyridyl leads to cation [(η5‐tetrahydrofluorenyl)Rh(2,2′‐bipyridyl)I]+ (3). The halide abstraction from 2 a,b with thallium or silver salts allowed us to prepare sandwich compounds with incoming cyclopentadienyl, dicarbollide and mesityleneligands [(η5‐tetrahydrofluorenyl)RhCp]+ (4), (η5‐tetrahydrofluorenyl)Rh(η‐7,8‐C2B9H11) (5), and [(η5‐tetrahydrofluorenyl)Rh(η‐mesitylene)]2+ (6). The structures of 1 b, 2 b ⋅ 2I2, 3PF6, 4TlI4, 5, and [(cod)RhI]2 were determined by X‐ray diffraction. Compounds 2 a,b efficiently catalyze the oxidative coupling of benzoic acids with alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature. Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation. Compound 2 b also effectively catalyzes the reductive amination of aldehydes and ketones in the presence of carbon monoxide and water via water‐gas shift reaction, giving amines in high yields (67–99 %). [ABSTRACT FROM AUTHOR]

Abstract Bis(indenyl)-rhodium and -iridium complexes [(η5-indenyl)M(η5-C 9 H 2 R 5)]PF 6 (2a : M = Rh, R = H; 2b : M = Ir, R = H; 3 : M = Rh, R = Me) were synthesized by reactions of iodides [(η5-indenyl)MI 2 ] n (1a , b) with indenes in the presence of AgPF 6. The structures of 2a SbF 6 and 2b PF 6 were determined by X-ray diffraction. They have fully eclipsed geometry, in which the bridgehead carbon atoms of the indenyl ligands are arranged close to each other. Experimental and DFT calculation data showed that the strength of the M−indenyl bond in the bis(indenyl) compounds decreases in the following row: Ir > Co > Rh. Graphical abstract Image 1 Highlights • A straightforward approach to bis(indenyl)-rhodium and -iridium complexes was developed. • X-ray diffraction suggested that they have a fully eclipsed cisoid conformation. • Correlation of 13C NMR chemical shifts with bond dissociation energy was proposed. [ABSTRACT FROM AUTHOR]

Catalytic reaction of arylhydroxamic acids with alkenes represents a convenient method for preparation of biologically active dihydroisoquinolones. Here, the rhodium(III) complex [(C5H2tBu2CH2tBu)RhCl2]2, which allows one to carry out such reactions with high regioselectivity to obtain 4‐substituted dihydroisoquinolones in 72–97 % yields, is described. The regioselectivity is provided by the bulky cyclopentadienyl ligand of the catalyst, which is formed through a [2+2+1] cyclotrimerization of tert‐butylacetylene. The catalytic reaction tolerates various distant functional groups in alkenes, but is inhibited by bulky (e.g., tBu) or strongly coordinating (e.g., imidazolyl) substituents. Some of the prepared dihydroisoquinolones effectively inhibit growth of phytopathogenic fungi. Regioselective synthesis of biologically active dihydroisoquinolones was achieved by using rhodium(III) catalyst with bulky cyclopentadienyl ligand, which was formed from three tert‐butylacetylenes. [ABSTRACT FROM AUTHOR]

Abstract: The rapid development of enantioselective C−H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar‐chiral rhodium catalyst [(C5H2tBu2CH2tBu)RhI2]2 in two steps from commercially available [(cod)RhCl]2 and tert‐butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)‐proline. The catalyst promoted enantioselective reactions of aryl hydroxamic acids with strained alkenes to give dihydroisoquinolones in high yields (up to 97 %) and with good stereoselectivity (up to 95 % ee). [ABSTRACT FROM AUTHOR]

In the original article, Scheme 5 describes the reaction of O-Boc-phenylhydroxamic acid with a mixture of alkenes, Scheme 6 describes the reaction of O-Boc- and O-Piv-phenylhydroxamic acid with styrene. For example, reaction of B 1 a b with an equimolar mixture of allyl alcohol, styrene and myrcene proceed selectively in the presence of the catalyst B 5 b to give 4-CH SB 2 sb OH-substituted product B 4 e b in 89 % yield (Scheme 5). Indeed, we observed that the reaction of O-Boc-phenylhydroxamic acid B 1 a b with styrene in the presence of the classical catalyst [Cp*RhCl SB 2 sb ] SB 2 sb gives only the 3-benzylisoindolin-1-one B 4 p b , while similar reaction of O-pivaloyl-phenylhydroxamic acid B 1 b b produced the 3-substituted structural isomer B 3 p b (Scheme 6). [Extracted from the article]

• General procedures to a family of half-sandwich complexes with N,Nʹ-ligands was developed. • The complexes efficiently catalyze the CF 3 -carbenoid alkylation of N-(pyrimidin-2-yl)indole. • The alkylation exclusively proceeds to C3 position of indole moiety. • 2,2′-Bipyridyl, 1,10-phenanthroline, and tris(pyrazolyl)borate anion were used as N,Nʹ-ligands. The complexes [CpM(N,Nʹ-ligand)Br]PF 6 (M = Rh, Ir; N,Nʹ-ligand = 2,2′-bipyridyl, 1,10-phenanthroline) were synthesized by reactions of bromides [CpMBr 2 ] n with 2,2′-bipyridyl or 1,10-phenanthroline followed by a counterion exchange. The replacement of cyclooctadiene in [CpIr(cod)I]I 3 with N,Nʹ-ligands leads to complexes [CpIr(N,Nʹ-ligand)I]I 3 (N,Nʹ-ligand = 2,2′-bipyridyl, 1,10-phenanthroline). The structures of [CpRh(2,2′-bipyridyl)Br]PF 6 , [CpIr(2,2′-bipyridyl)I]I 3 , and [CpIr(1,10-phenanthroline)Br]PF 6 were determined by X-ray diffraction. The compounds prepared as well as the related the tris(pyrazolyl)borate derivatives [CpCoTp]PF 6 and [Cp*MTp]PF 6 (M = Rh, Ir) efficiently catalyze the alkylation of N-(pyrimidin-2-yl)indole with methyl 3,3,3-trifluoro-2-diazopropionate to selectively introduce the CF 3 and carboxylate functions at the C3 position of the indole moiety. In contrast, the tris(pyrazolyl)borate cobalt complex [Cp*CoTp]PF 6 predominantly provides the alkylation at the C2 position. [Display omitted] [ABSTRACT FROM AUTHOR]

Reaction of two molecules of o‐diphenylphosphino‐tolane with RhCl(PPh3)3 produces the metallacycle complex with C4Rh(P3)Cl core. Further addition of tolane leads to 2+2+2‐cycloaddition and gives the cationic complex [Rh(Ph2P−C6H4−C6Ph4−C6H4−PPh2)]Cl, in which the metal is coordinated to C6Ph4 aromatic ring as well to two chelating PPh2 groups. The resulting bulky terphenyl‐diphosphine ligand with phosphorous atoms locked in cis‐position can be decoordinated from rhodium by a strong and non‐hindered ligand tBuNC. Peculiar structures of all the compounds were studied by the X‐ray diffraction. [ABSTRACT FROM AUTHOR]

[Display omitted] Porous metal–organic framework ZIF-8 materials containing incorporated rhodium (Rh@ZIF-8) and rhodium chloride (RhCl 3 @ZIF-8) nanoparticles were obtained and tested as a catalytic reaction vessel in the reactions of hydroformylation of 1-decene and styrene. Catalytic tests with Rh@ZIF-8 showed that the selectivity and conversion of the hydroformylation reaction depended on the size of the substrate molecule. The incorporation of catalytic nanoparticles into the pores of a metal–organic framework opens up new possibilities for regioselective hydroformylation. [ABSTRACT FROM AUTHOR]

A page of a coloring book shows the molecules of hydroxamic acid and alkene at the fork of the road. The signpost with a traditional weathervane figure—the cyclopentadienyl rhodium catalyst—directs the reaction to the right to give the 4‐substituted dihydroisoquinolones. For more information, see the Full Paper by D. S. Perekalin et al. on page 16570 ff. [ABSTRACT FROM AUTHOR]

Sandwich Complexes The center of the stained glass represents the top view of the cyclobutadiene rhodium benzene complex [(C4H4)Rh(C6H6)]+. This sandwich compound not only shows the geometric beauty (circle inscribed in a square inscribed in a hexagon!) but also provides an entry to the world of the cyclobutadiene rhodium complexes through replacement of benzene by various ligands. Details of this research is reported by A. R. Kudinov and co ‐ workers in their Communication on page 16344 ff. [ABSTRACT FROM AUTHOR]

In a search for an active catalyst for CH-activation reactions we have synthesized the half-sandwich rhodium complexes with a cyclohexadienyl ligand. In particular, the reaction of [(cyclooctene) 2 RhCl] 2 with 1,3,5,5-tetramethylcyclohexadiene followed by addition of bromine gave the cyclohexadienyl polybromide complex [(η 5 -C 6 H 3 Me 4 )RhBr 3 ] n ( 1 ) in 73% yield. Treatment of 1 with ethylene converted it into the Rh(III) bromide complex [(η 5 -C 6 H 3 Me 4 )RhBr 2 ] 2 ( 2 ), which is analogous to the classical catalyst [Cp*RhCl 2 ] 2 . The reaction of 2 with 2 equiv. of 2-electron ligands L produced the expected adducts (η 5 -C 6 H 3 Me 4 )RhBr 2 L (L =  t BuNC, pyridine, P(OMe) 3 , PPh 3 ) in 80–90% yields. On the other hand, the reactions of 1 or 2 with excess of t BuNC led to complete replacement of the cyclohexadienyl ligand. The complex 2 was found to be inactive as catalyst (at 10 mol-% loading) for reactions of diphenylacetylene with benzoic acid, acetanilide, O-Boc-phenylhydroxamic acid, or benzophenone oxime. The absence of catalytic activity was attributed to the displacement of the cyclohexadienyl ligand. [ABSTRACT FROM AUTHOR]

The halide complexes TpRhCl 2 (MeOH) and TpMe2RhI 2 (CO) (Tp = hydrotris-(pyrazolyl)borate; TpMe2 = hydrotris-(3,5-dimethylpyrazolyl)borate) were synthesized by reactions of RhCl 3 with K[Tp] in methanol and TpMe2Rh(CO) 2 with iodine, respectively. Reactions of TpMe2RhCl 2 (MeOH) and TpMe2RhI 2 (CO) with 1,10-phenanthroline afford the phenanthroline derivatives [TpMe2Rh(phen)X]+ (X = Cl, I). The structures of TpRhCl 2 (MeOH) and TpRhI 2 (CO) were determined by X-ray diffraction. Tris(pyrazolyl)borate rhodium complexes effectively catalyze the reductive amination and the reductive esterification of aldehydes in the presence of carbon monoxide. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Reactions of [(C2H4)2RhCl]2 or [(coe)2RhCl]2 (coe = cyclooctene) with AgPF6 and arenes, followed by addition of 3-hexyne, give the cyclobutadiene complexes [(C4Et4)Rh(arene)]+ in 40-65% yield (arene = tert-butylbenzene, p-xylene, mesitylene, 4-mesitylbutanoic acid). In the absence of arenes, the hexaethylbenzene complex [(C4Et4)Rh(C6Et6)]+ is formed in 70% yield as a result of cyclotrimerization of 3-hexyne in the coordination sphere of rhodium. Similar reaction of [(coe)2IrCl]2 with AgPF6 and 3-hexyne leads to [(C4Et4)Ir(C6Et6)]+, which is apparently the first reported cyclobutadiene iridium complex. DFT calculations suggest that formation of the model cyclobutadiene complex [(C4Me4)Rh(C6H6)]+ from bis(alkyne) intermediate [(C2Me2)2Rh(C6H6)]+ can proceed via a metallacycle transition state with a low energy barrier of 14.5 kcal mol-1. [ABSTRACT FROM AUTHOR]