Facile Synthetic Access to Rhenium(II) Complexes: Activation of Carbon–Bromine Bonds by Single‐Electron Transfer

The five‐coordinated Re^I hydride complexes [Re(Br)(H)(NO)(PR₃)₂] (R=Cy 1 a , iPr 1 b ) were reacted with benzylbromide, thereby affording the 17‐electron mononuclear Re^II hydride complexes [Re(Br)₂(H)(NO)(PR₃)₂] (R=Cy 3 a , iPr 3 b ), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded Re^II hydrides 3 in addition to Re^I carbene hydrides [Re(?CHR¹)(Br)(H)(NO)(PR₃)₂] (R¹=H 4 , Br 5 ; R=Cy a , iPr b ) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen Re^I dibromide complexes [Re(Br)₂(NO)(PR₃)₂(η²‐H₂)] (R=Cy 2 a , iPr 2 b ) were reacted with allyl‐ or benzylbromide, thereby affording the monophosphine Re^II complex salts [R₃PCH₂R′][Re(Br)₄(NO)(PR₃)] (R′=? CH?CH₂ 6 , Ph 7 ). The reduction of Re^II complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford 1 a or 1 b in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3 a 150, 3 b 134 h^?1) or allylbromide (TOF: 3 a 575, 3 b 562 h^?1). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine Re^I complexes [Re(Br)₂(NO)(MeCN)₂(PR₃)] (R=Cy 8 a , iPr 8 b ), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h^?1). Single‐electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a , 6 a , 6 b , 7 a , 7 b , and 8 a were established by single‐crystal X‐ray diffraction studies.     

Binding H2, N2, H-, and BH3 to transition-metal sulfur sites: synthesis and properties of [RuL(PR3)(N2Me2S2)] Complexes (L=eta2-H2, H-, BH3; R=Cy, iPr)

The reactions of [Ru(N₂)(PR₃)(‘N₂Me₂S₂’)] [‘N₂Me₂S₂’=1,2‐ethanediamine‐N,N′‐dimethyl‐N,N′‐bis(2‐benzenethiolate)(2?)] [ 1 a (R=iPr), 1 b (R=Cy)] and [μ‐N₂{Ru(N₂)(PiPr₃)(‘N₂Me₂S₂’)}₂] ( 1 c ) with H₂, NaBH₄, and NBu₄BH₄, intended to reduce the N₂ ligands, led to substitution of N₂ and formation of the new complexes [Ru(H₂)(PR₃)(‘N₂Me₂S₂’)] [ 2 a (R=iPr), 2 b (R=Cy)], [Ru(BH₃)(PR₃)(‘N₂Me₂S₂’)] [ 3 a (R=iPr), 3 b (R=Cy)], and [Ru(H)(PR₃)(‘N₂Me₂S₂’)]^? [ 4 a (R=iPr), 4 b (R=Cy)]. The BH₃ and hydride complexes 3 a , 3 b , 4 a , and 4 b were obtained subsequently by rational synthesis from 1 a or 1 b and BH₃?THF or LiBEt₃H. The primary step in all reactions probably is the dissociation of N₂ from the N₂ complexes to give coordinatively unsaturated [Ru(PR₃)(‘N₂Me₂S₂’)] fragments that add H₂, BH₄^?, BH₃, or H^?. All complexes were completely characterized by elemental analysis and common spectroscopic methods. The molecular structures of [Ru(H₂)(PR₃)(‘N₂Me₂S₂’)] [ 2 a (R=iPr), 2 b (R=Cy)], [Ru(BH₃)(PiPr₃)(‘N₂Me₂S₂’)] ( 3 a ), [Li(THF)₂][Ru(H)(PiPr₃)(‘N₂Me₂S₂’)] ([Li(THF)₂]‐ 4 a ), and NBu₄[Ru(H)(PCy₃)(‘N₂Me₂S₂’)] (NBu₄‐ 4 b ) were determined by X‐ray crystal structure analysis. Measurements of the NMR relaxation time T₁ corroborated the η² bonding mode of the H₂ ligands in 2 a (T₁=35 ms) and 2 b (T₁=21 ms). The H,D coupling constants of the analogous HD complexes HD‐ 2 a (¹J(H,D)=26.0 Hz) and HD‐ 2 b (¹J(H,D)=25.9 Hz) enabled calculation of the H? D distances, which agreed with the values found by X‐ray crystal structure analysis ( 2 a : 92 pm (X‐ray) versus 98 pm (calculated), 2 b : 99 versus 98 pm). The BH₃ entities in 3 a and 3 b bind to one thiolate donor of the [Ru(PR₃)(‘N₂Me₂S₂’)] fragment and through a B‐H‐Ru bond to the Ru center. The hydride complex anions 4 a and 4 b are extremely Brønsted basic and are instantanously protonated to give the η²‐H₂ complexes 2 a and 2 b .     

Highly Selective Dehydrogenative Silylation of Alkenes Catalyzed by Rhenium Complexes

Choosy chemicals : Rhenium(I) complexes of type [ReBr₂(L)(NO)(PR₃)₂] (L=H₂ ( 1 ), CH₃CN ( 2 ), ethylene ( 3 ); R=iPr ( a ), cyclohexyl ( b )) proved to be suitable catalyst precursors for the highly selective dehydrogenative silylation of alkenes. Two types of rhenium(I) hydride species, [ReBrH(NO)(PR₃)₂] ( 4 ) and [ReBr(η²‐CH₂?CHR¹)H(NO)(PR₃)₂] ( 5 ), were found in the [ReBr₂(L)(NO)(PR₃)₂]‐catalyzed dehydrogenative silylation of alkenes.

     

Synthese,Struktur und Photochemie von Olefiniridium(I)‐Komplexen mit Acetylacetonatoliganden

Synthesis, Structure, and Photochemical Behavior of Olefine Iridium(I) Complexes with Acetylacetonato Ligands The bis(ethene) complex [Ir(κ²‐acac)(C₂H₄)₂] ( 1 ) reacts with tertiary phosphanes to give the monosubstitution products [Ir(κ²‐acac)(C₂H₄)(PR₃)] ( 2 – 5 ). While 2 (R = iPr) is inert toward PiPr₃, the reaction of 2 with diphenylacetylene affords the π‐alkyne complex [Ir(κ²‐acac)(C₂Ph₂)(PiPr₃)] ( 6 ). Treatment of [IrCl(C₂H₄)₄] with C‐functionalized acetylacetonates yields the compounds [Ir(κ²‐acacR^1,2)(C₂H₄)₂] ( 8 , 9 ), which react with PiPr₃ to give [Ir(κ²‐acacR^1,2)(C₂H₄)(PiPr₃)] ( 10 , 11 ) by displacement of one ethene ligand. UV irradiation of 5 (PR₃ = iPr₂PCH₂CO₂Me) and 11 (R² = (CH₂)₃CO₂Me) leads, after addition of PiPr₃, to the formation of the hydrido(vinyl)iridium(III) complexes 7 and 12 . The reaction of 2 with the ethene derivatives CH₂=CHR (R = CN, OC(O)Me, C(O)Me) affords the compounds [Ir(κ²‐acac)(CH₂=CHR)(PiPr₃)] ( 13 – 15 ), which on photolysis in the presence of PiPr₃ also undergo an intramolecular C–H activation. In contrast, the analogous complexes [Ir(κ²‐acac)(olefin)(PiPr₃)] (olefin = (E)‐C₂H₂(CO₂Me)₂ 16 , (Z)‐C₂H₂(CO₂Me)₂ 17 ) are photochemically inert.     

Bifunctional rhenium complexes for the catalytic transfer-hydrogenation reactions of ketones and imines

The silyloxycyclopentadienyl hydride complexes [Re(H)(NO)(PR(3))(C(5)H(4)OSiMe(2)tBu)] (R=iPr (3 a), Cy (3 b)) were obtained by the reaction of [Re(H)(Br)(NO)(PR(3))(2)] (R=iPr, Cy) with Li[C(5)H(4)OSiMe(2)tBu]. The ligand-metal bifunctional rhenium catalysts [Re(H)(NO)(PR(3))(C(5)H(4)OH)] (R=iPr (5 a), Cy (5 b)) were prepared from compounds 3 a and 3 b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts [Re(H)(NO)(PR(3))(C(5)H(4)O)][NBu(4)] (R=iPr (4 a), Cy (4 b)) with NH(4)Br. In nonpolar solvents, compounds 5 a and 5 b formed an equilibrium with the isomerized trans-dihydride cyclopentadienone species [Re(H)(2)(NO)(PR(3))(C(5)H(4)O)] (6 a,b). Deuterium-labeling studies of compounds 5 a and 5 b with D(2) and D(2)O showed H/D exchange at the H(Re) and H(O) positions. Compounds 5 a and 5 b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2-propanol as both the solvent and H(2) source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary-coordination-sphere mechanism for the transfer hydrogenation of ketones.     

Latent cationic palladium(II) phosphine carboxylate complexes for norbornene polymerization

The catalytic efficacy of trans‐[(R₃P)₂Pd(O₂CR′)(LB)][B(C₆F₅)₄] ( 1 ) (LB = Lewis base) and [(R₃P)₂Pd(κ²‐O,O‐O₂CR′)][B(C₆F₅)₄] ( 2 ) for mass polymerization of 5‐n‐butyl‐2‐norbornene (Butyl‐NB) was investigated. The nature of PR₃ and LB in 1 and 2 are the most critical components influencing catalytic activity/latency for the mass polymerization of Butyl‐NB. Further, it was shown that 1 is in general more latent than 2 in mass polymerization of Butyl‐NB. 5‐n‐Decyl‐2‐norbornene (Decyl‐NB) was subjected to solution polymerization in toluene at 63(±3) °C in the presence of several of the aforementioned palladium complexes as catalysts and the polymers obtained were characterized by gel permeation chromatography. Cationic trans‐[(R₃P)₂PdMe(MeCN)][B(C₆F₅)₄] [R = Cy ( 3a ), and ⁱPr ( 3b )] and trans‐[(R₃P)₂PdH (MeCN)][B(C₆F₅)₄] [R = Cy ( 4a ), and ⁱPr ( 4b )], possible products from thermolysis of trans‐[(R₃P)₂Pd(O₂CMe)(MeCN)][B(C₆F₅)₄] [R = Cy ( 1a ) and ⁱPr ( 1g )], as well as trans‐[(R₃P)₂Pd(η³‐C₃H₅)][B(C₆F₅)₄] [R = Cy ( 5a ), and ⁱPr ( 5b )], were also examined as catalysts for solution polymerization of Decyl‐NB. A maximum activity of 5360 kg/(molPd h) of 2a was achieved at a Decyl‐NB/Pd: 26,700 ratio which is slightly better than that achieved with 5a [activity: 5030 kg/(molPd h)] but far less compared with 4a [activity: 6110 kg/(molPd h)]. Polydispersity values indicate a single highly homogeneous character of the active catalyst species. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 103–110, 2009     

Activation of SF6 at Platinum Complexes: Formation of SF3 Derivatives and Their Application in Deoxyfluorination Reactions

The activation of SF₆ at [Pt(PR₃)₂] R=Cy, i Pr complexes in the presence of PR₃ led selectively and in an unprecedented reaction route to the generation of the SF₃ complexes trans ‐[Pt(F)(SF₃)(PR₃)₂]. These can also be synthesized from SF₄ and the SF₂ derivative trans ‐[Pt(F)(SF₂)(PCy₃)₂][BF₄] was characterized by X‐ray crystallography. trans ‐[Pt(F)(SF₃)(PR₃)₂] complexes are useful tools for deoxyfluorination reactions and novel fluorido complexes bearing a SOF ligand are formed. Based on these studies a process for the deoxyfluorination of ketones was developed with SF₆ as fluorinating agent.     

Synthesis,Structure, and Reactivity of Hydridoiridium Complexes Bearing a Pincer‐Type PSiP Ligand

A series of iridium tetrahydride complexes [Ir(H)₄(PSiP‐R)] bearing a tridentate pincer‐type bis(phosphino)silyl ligand ([{2‐(R₂P)C₆H₄}₂MeSi]⁻, PSiP‐R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP‐R)] with Me₄N ⋅ BH₄ under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)–dinitrogen complexes, [Ir(H)₂(N₂)(PSiP‐R)]. Two isomeric dinitrogen complexes were produced, in which the PSiP ligand coordinated to the iridium center in meridional and facial orientations, respectively. Attempted substitution of the dinitrogen ligand in [Ir(H)₂(N₂)(PSiP‐Cy)] with PMe₃ required heating at 150 °C to give the expected [Ir(H)₂(PMe₃)(PSiP‐Cy)] and a trigonal bipyramidal iridium(I)–dinitrogen complex, [Ir(N₂)(PMe₃)(PSiP‐Cy)]. The reaction of [Ir(H)₄(PSiP‐Cy)] with three equivalents of 2‐norbornene (nbe) in benzene afforded [Ir^I(nbe)(PSiP‐Cy)] in a high yield, while a similar reaction of [Ir(H)₄(PSiP‐R)] with an excess of 3,3‐dimethylbutene (tbe) in benzene gave the C H bond activation product, [Ir^III(H)(Ph)(PSiP‐R)], in high yield. The oxidative addition of benzene is reversible; heating [Ir^III(H)(Ph)(PSiP‐Cy)] in the presence of PPh₃ in benzene resulted in reductive elimination of benzene, coordination of PPh₃, and activation of the C H bond of one aromatic ring in PPh₃. [Ir^III(H)(Ph)(PSiP‐R)] catalyzed a direct borylation reaction of the benzene C H bond with bis(pinacolato)diboron. Molecular structures of most of the new complexes in this study were determined by a single‐crystal X‐ray analysis.     

The reactions of [Co(η-C5H5)(CO)(L)] (L = R3P or RNC) with carbon disuphide and organoisothiocyanates

The reactions of [Co(η-C₅H₅)(CO)(PR₃)] or [Co(η-C₅GH₅)(CO)₂]/R₃P mixtures (R = alkyl or aryl) with CS₂ in refluxing CS₂ or CS₂/toluene gives rise to [Co(η-C₅H₅)(PR₃)(CS)], [Co(η-C₅H₅)(PR₃)(CS₂)], [Co(η-C₅H₅)(PR₃)(CS₃)], and [Co₃(η-C₅H₅)₃ (CS)(S)] in reasonable yields. The corresponding reactions using PhNCS give [Co(η-C₅H₅)(PPh₃)(PhNCS)] and a polymeric species which appears to be [Co₄(η-C₅H₅)₄ (PhNCS)]. Similar products are obtained with [Co(η-C₅H₅)(CO)(CNR)] or [Co(η0C₅H₅)(CO)₂]/RNC mixtures.     

Synthesis and Reactivity of Iridium(I) Fluorido Complexes: Oxidative Addition of SF4 at trans-[Ir(F)(CO)(PEt3)2]

The facile access to the Vaska type fluorido complexes trans-[Ir(F)(CO)(PR₃)₂] [ 6 : R = Et, 7 : R = Ph, 8 : R = iPr, 9 : R = Cy, 10 : R = tBu] was achieved by halide exchange at trans-[Ir(Cl)(CO)(PR₃)₂] ( 1 – 5 ) with Me₄NF. Furthermore, the reaction of complex 6 with SF₄ gave cis,trans-[Ir(F)₂(SF₃)(CO)(PEt₃)₂] ( 11 ), whereas 8 – 10 did not react. Reactivity studies revealed that 11 can selectively be manipulated at the sulfur atom by hydrolysis or fluoride abstraction to give cis,trans-[Ir(F)₂(SOF)(CO)(PEt₃)₂] ( 12 ) and cis,trans-[Ir(F)₂(SF₂)(CO)(PEt₃)₂][AsF₆] ( 13 ), respectively.     

Reactions of [Re(NO)2(PR3)2][BArF 4] complexes with phenylacetylene

The reaction of [Re(NO)₂(PR₃)₂][BAr^F ₄] (R = cyclo-C₆H₁₃ (1a), Prⁱ (1b); [BAr^F ₄]^– = [B(3,5-(CF₃)₂C₆H₃)₄]) with phenylacetylene in the presence of a non-nucleophilic base, like 2,6-bis(tert-butyl)pyridine (BTBP) or Bu^tOK, affords the phenylethynyl complexes [Re(CCPh)(NO)₂(PR₃)₂] (R = cyclo-C₆H₁₃ (2a); Prⁱ (2b)) in moderate yields. In the absence of a base, complexes 1a and 1b are transformed into the compounds [Re(CCPh)(CH=C(Ph)ONH)(NO)(PR₃)₂][BAr^F ₄] (3a and 3b, respectively). The structure of complex 3a was confirmed by X-ray diffraction analysis. The latter reaction is proposed to be initiated by deprotonation of the terminal alkyne H atom by the bent nitrosyl ligand followed by the subsequent 1,3-dipolar addition of the ReN(H)O moiety to phenylacetylene.     

Germylene Cyanide Complex: A Reagent for the Activation of Aldehydes with Catalytic Significance

The first example of a germanium(II) cyanide complex [GeCN(L)] ( 2 ) (L=aminotroponiminate (ATI)) has been synthesized through a novel and relatively benign route that involves the reaction of a digermylene oxide [(L)Ge?O?Ge(L)] ( 1 ) with trimethylsilylcyanide (TMSCN). Interestingly, compound 2 activates several aldehydes (RCHO) at room temperature and results in the corresponding cyanogermylated products [RC{OGe(L)}(CN)H] (R=H 3 , iPr 4 , tBu 5 , CH(Ph)Me 6 ). Reaction of one of the cyanogermylated products ( 4 ) with TMSCN affords the cyanosilylated product [(iPr)C(OSiMe₃)(CN)H] ( 7 ) along with [GeCN(L)] quantitatively, and insinuates the possible utility of [GeCN(L)] as a catalyst for the cyanosilylation reactions of aldehydes with TMSCN. Accordingly, the quantitative formation of several cyanosilylated products [RC(OSiMe₃)(CN)H] ( 7 – 9 ) in the reaction between RCHO and TMSCN by using 1 mol % of [GeCN(L)] as a catalyst is also reported for the first time.     

Iridium(I)‐ und Iridium(III)‐Komplexe mit Triisopropylarsan als Ligand

Iridium(I) and Iridium(III) Complexes with Triisopropylarsane as Ligand The ethene complex trans‐[IrCl(C₂H₄)(AsiPr₃)₂] ( 2 ), which was prepared from [IrCl(C₂H₄)₂]₂ and AsiPr₃, reacted with CO and Ph₂CN₂ by displacement of ethene to yield the substitution products trans‐[IrCl(L)(AsiPr₃)₂] ( 3 : L = CO; 4 : L = N₂). UV irradiation of 2 in the presence of acetonitrile gave via intramolecular oxidative addition the hydrido(vinyl)iridium(III) compound [IrHCl(CH=CH₂)(CH₃CN)(AsiPr₃)₂] ( 5 ). The reaction of 2 with dihydrogen led under argon to the formation of the octahedral complex [IrH₂Cl(C₂H₄)(AsiPr₃)₂] ( 7 ), whereas from 2 under 1 bar H₂ the ethene‐free compound [IrH₂Cl(AsiPr₃)₂] ( 6 ) was generated. Complex 6 reacted with ethene to afford 7 and with pyridine to give [IrH₂Cl(py)(AsiPr₃)₂] ( 8 ). The mixed arsane(phosphane)iridium(I) compound [IrCl(C₂H₄)(PiPr₃)(AsiPr₃)] ( 11 ) was prepared either from the dinuclear complex [IrCl(C₂H₄)(PiPr₃)]2 ( 9 ) and AsiPr₃ or by ligand exchange from [IrCl(C₂H₄)(PiPr₃)(SbiPr₃)] ( 10 ) und triisopropylarsane. The molecular structure of 5 was determined by X‐ray crystallography.     

Synthese,Struktur und Reaktivität von η3‐1,2‐Diphosphaallylkomplexen sowie von [{(η5‐C5H5)(CO)2W–Co(CO)3}{μ‐AsCH(SiMe3)2}(μ‐CO)]

Syntheses, Structure and Reactivity of η³‐1,2‐Diphosphaallyl Complexes and [{(η⁵‐C₅H₅)(CO)₂W–Co(CO)₃}{μ‐AsCH(SiMe₃)₂}(μ‐CO)] Reaction of ClP=C(SiMe₂iPr)₂ ( 3 ) with Na[Mo(CO)₃(η⁵‐C₅H₅)] afforded the phosphavinylidene complex [(η⁵‐C₅H₅)(CO)₂Mo=P=C(SiMe₂iPr)₂] ( 4 ) which in situ was converted into the η¹‐1,2‐diphosphaallyl complex [η⁵‐(C₅H₅)(CO)₂Mo{η³‐tBuPPC(SiMe₂iPr)₂] ( 6 ) by treatment with the phosphaalkene tBuP=C(NMe₂)₂. The chloroarsanyl complexes [(η⁵‐C₅H₅)(CO)₃M–As(Cl)CH(SiMe₃)₂] [where M = Mo ( 9 ); M = W ( 10 )] resulted from the reaction of Na[M(CO)₃(η⁵‐C₅H₅)] (M = Mo, W) with Cl₂AsCH(SiMe₃)₂. The tungsten derivative 10 and Na[Co(CO)₄] underwent reaction to give the dinuclear μ‐arsinidene complex [(η⁵‐C₅H₅)(CO)₂W–Co(CO)₃{μ‐AsCH(SiMe₃)₂}(μ‐CO)] ( 11 ). Treatment of [(η⁵‐C₅H₅)(CO)₂Mo{η³‐tBuPPC(SiMe₃)₂}] ( 1 ) with an equimolar amount of ethereal HBF₄ gave rise to a 85/15 mixture of the saline complexes [(η⁵‐C₅H₅)(CO)₂Mo{η²‐tBu(H)P–P(F)CH(SiMe₃)₂}]BF₄ ( 18 ) and [Cp(CO)₂Mo{F₂PCH(SiMe₃)₂}(tBuPH₂)]BF₄ ( 19 ) by HF‐addition to the PC bond of the η³‐diphosphaallyl ligand and subsequent protonation ( 18 ) and/or scission of the PP bond by the acid ( 19 ). Consistently 19 was the sole product when 1 was allowed to react with an excess of ethereal HBF₄. The products 6 , 9 , 10 , 11 , 18 and 19 were characterized by means of spectroscopy (IR, ¹H‐, ¹³C{¹H}‐, ³¹P{¹H}‐NMR, MS). Moreover, the molecular structures of 6 , 11 and 18 were determined by X‐ray diffraction analysis.     

Versatile reactivity of half-sandwich Ir and Rh complexes toward carboranylamidinates and their derivatives: synthesis, structure, and catalytic activity for norbornene polymerization

Synthesis, structure, and reactivity of carboranylamidinate‐based half‐sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ‐Cl)Cl}₂] (M=Ir, Rh; Cp*=η⁵‐C₅Me₅) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18‐electron complexes [Cp*IrCl(Cab^N‐DIC)] ( 1 a ; Cab^N‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHiPr)]), [Cp*RhCl(Cab^N‐DIC)] ( 1 b ), and [Cp*RhCl(Cab^N‐DCC)] ( 1 c ; Cab^N‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHCy)]). A series of 16‐electron half‐sandwich Ir and Rh complexes [Cp*Ir(Cab^N′‐DIC)] ( 2 a ; Cab^N′‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NiPr)]), [Cp*Ir(Cab^N′‐DCC)] ( 2 b , Cab^N′‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NCy)]), and [Cp*Rh(Cab^N′‐DIC)] ( 2 c ) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab^N,S‐DIC)], [Cp*M(Cab^N,S‐DCC)] (M=Ir 3 a , 3 b ; Rh 3 c , 3 d ), formed through BH activation, are obtained by reaction of [{Cp*MCl₂}₂] with carboranylamidinate sulfides [RN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHR)]S^? (R=iPr, Cy), which can be prepared by inserting sulfur into the C? Li bond of lithium carboranylamidinates. Iridium complex 1 a shows catalytic activities of up to 2.69×10⁶ g_PNB ${{\rm{mol}}_{{\rm{Ir}}}^{ - {\rm{1}}} }Synthesis, structure, and reactivity of carboranylamidinate-based half-sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ-Cl)Cl}(2)] (M = Ir, Rh; Cp* = η(5)-C(5)Me(5)) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18-electron complexes [Cp*IrCl(Cab(N)-DIC)] (1?a; Cab(N)-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NHiPr)]), [Cp*RhCl(Cab(N)-DIC)] (1?b), and [Cp*RhCl(Cab(N)-DCC)] (1?c; Cab(N)-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10))(NHCy)]). A series of 16-electron half-sandwich Ir and Rh complexes [Cp*Ir(Cab(N')-DIC)] (2?a; Cab(N')-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NiPr)]), [Cp*Ir(Cab(N')-DCC)] (2?b, Cab(N')-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10)(NCy)]), and [Cp*Rh(Cab(N')-DIC)] (2?c) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab(N,S)-DIC)], [Cp*M(Cab(N,S)-DCC)] (M = Ir 3?a, 3?b; Rh 3?c, 3?d), formed through BH activation, are obtained by reaction of [{Cp*MCl(2)}(2)] with carboranylamidinate sulfides [RN=C(closo-1,2-C(2)B(10)H(10))(NHR)]S(-) (R = iPr, Cy), which can be prepared by inserting sulfur into the C-Li bond of lithium carboranylamidinates. Iridium complex 1?a shows catalytic activities of up to 2.69×10(6) g(PNB) mol(Ir)(-1) h(-1) for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities and the molecular weight of polynorbornene (PNB) were investigated under various reaction conditions. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy; the structures of 1?a-c, 2?a, b; and 3?a, b, d were further confirmed by single crystal X-ray diffraction.     

Regioselektive Ringöffnungen von einfach ungesättigten triangularen Clusterkomplexen [M2Rh(μ‐PR2)(μ‐CO)2(CO)8] (M2 = Re2, Mn2; R = Cy,Ph; M2 = MnRe,R = Ph) mit Diphosphanen

Regioselective Ring Opening Reactions of Unifold Unsaturated Triangular Cluster Complexes [M₂Rh(μ‐PR₂)(μ‐CO)₂(CO)₈] (M₂ = Re₂, Mn₂; R = Cy, Ph; M₂ = MnRe, R = Ph) with Diphosphanes Equimolar amounts of the triangular title compounds and chelates of the type (Ph₂P)₂Z (Z = CH₂, DPPM ; C=CH₂, EPP ) react in thf solution at –40 to –20 °C under release of the labile terminal carbonyl ligand attached to the rhodium atom in good yields (70–90%) to ring‐opened unifold unsaturated complexes [MRh(μ‐PR₂)(CO)₄M(DPPM bzw. EPP)(μ‐CO)₂(CO)₃] (DPPM: M₂ = Re₂, R = Cy 1 , Ph 2 ; Mn₂, Cy 5 , Ph 6 ; MnRe, Cy 7 . EPP: M₂ = Re₂, R = Cy 8 ; Mn₂, Cy 10 ). Complexes 1 , 2 and 8 react subsequently under minor uptake of carbon monoxide and formation of the valence saturated complexes [ReRh(μ‐PR₂)(CO)₄M(DPPM bzw. EPP) (CO)₆] (DPPM: R = Cy 3 , Ph 4 . EPP: R = Cy 9 ). Separate experiments ascertained that the regioselective ring opening at the M–M‐edge of the title compounds is limited to reactions with diphosphanes chelates with only one chain member and that the preparation of the unsaturated complexes demands relatively good donor ability of both P atoms. As examples for both types of compounds the molecular structures of 8 and 3 have been determined from single crystal X‐ray structure analysis. Additionally all new compounds are identified by means of ν(CO)IR, ¹H‐ and ³¹P‐NMR data. This includes complexes with a modified chain member in 1 and 5 which, after deprotonation reaction to carbanionic intermediates, could be trapped with [PPh₃Au]⁺ cations as rac‐[MRh(μ‐PR₂)(CO)₄M((Ph₂P)₂CHAuPPh₃)(μ‐CO)₂(CO)₃] (M₂ = Re 17 , Mn 18 ) and products rac‐[MRh(μ‐PR₂)(CO)₄M((Ph₂P)₂CHCH₂R)(μ‐CO)₂(CO)₃] (M₂ = Re, R = Ph 19 , n‐Bu 21 , Me 23 ; Mn, Ph 20 , n‐Bu 22 , Me 24 ) which result from Michael‐type addition reactions of 8 or 10 with strong nucleophiles LiR.     

Structural and energetic aspects of hydrogen bonding and proton transfer to ReH2(CO)(NO)(PR3)2 and ReHCl(CO)(NO)(PMe3)2 by IR and X-ray studies

The interaction of rhenium hydrides ReHX(CO)(NO)(PR₃)₂ 1 (X=H, R=Me (a), Et (b), iPr (c); X=Cl, R=Me (d)) with a series of proton donors (indole, phenols, fluorinated alcohols, trifluoroacetic acid) was studied by variable temperature IR spectroscopy. The conditions governing the hydrogen bonding ReHHX in solution and in the solid state (IR, X-ray) were elucidated. Spectroscopic and thermodynamic characteristics (−ΔH=2.3–6.1 kcal mol⁻¹) of these hydrogen bonded complexes were obtained. IR spectral evidence that hydrogen bonding with hydride atom precedes proton transfer and the dihydrogen complex formation was found. Hydrogen bonded complex of ReH₂(CO)(NO)(PMe₃)₂ with indole (2a–indole) and organyloxy-complex ReH(OC₆H₄NO₂)(CO)(NO)(PMe₃)₂ (5a) were characterized by single-crystal X-ray diffraction. A short NHHRe (1.79(5) Å) distance was found in the 2a–indole complex, where the indole molecule lies in the plane of the Re(NO)(CO) fragment (with dihedral angle between the planes 0.01°).     

Highly Active,Low‐Valence Molybdenum‐ and Tungsten‐Amide Catalysts for Bifunctional Imine‐Hydrogenation Reactions

The reactions of [M(NO)(CO)₄(ClAlCl₃)] (M=Mo, W) with (iPr₂PCH₂CH₂)₂NH, (PN^HP) at 90 °C afforded [M(NO)(CO)(PN^HP)Cl] complexes (M=Mo, 1a ; W, 1b ). The treatment of compound 1a with KOtBu as a base at room temperature yielded the alkoxide complex [Mo(NO)(CO)(PN^HP)(OtBu)] ( 2a ). In contrast, with the amide base Na[N(SiMe₃)₂], the PN^HP ligand moieties in compounds 1a and 1b could be deprotonated at room temperature, thereby inducing dehydrochlorination into amido complexes [M(NO)(CO)(PNP)] (M=Mo, 3a ; W, 3b ; PNP=(iPr₂PCH₂CH₂)₂N)). Compounds 3a and 3b have pseudo‐trigonal‐bipyramidal geometries, in which the amido nitrogen atom is in the equatorial plane. At room temperature, compounds 3a and 3b were capable of adding dihydrogen, with heterolytic splitting, thereby forming pairs of isomeric amine‐hydride complexes [Mo(NO)(CO)H(PN^HP)] ( 4a(cis) and 4a(trans) ) and [W(NO)(CO)H(PN^HP)] ( 4b(cis) and 4b(trans) ; cis and trans correspond to the position of the H and NO groups). H₂ approaches the Mo/W?N bond in compounds 3a , 3b from either the CO‐ligand side or from the NO‐ligand side. Compounds 4a(cis) and 4a(trans) were only found to be stable under a H₂ atmosphere and could not be isolated. At 140 °C and 60 bar H₂, compounds 3a and 3b catalyzed the hydrogenation of imines, thereby showing maximum turnover frequencies (TOFs) of 2912 and 1120 h^?1, respectively, for the hydrogenation of N‐(4 ‐ methoxybenzylidene)aniline. A Hammett plot for various para‐substituted imines revealed linear correlations with a negative slope of ?3.69 for para substitution on the benzylidene side and a positive slope of 0.68 for para substitution on the aniline side. Kinetics analysis revealed the initial rate of the hydrogenation reactions to be first order in c(cat.) and zeroth order in c(imine). Deuterium kinetic isotope effect (DKIE) experiments furnished a low k_H/k_D value (1.28), which supported a Noyori‐type metal–ligand bifunctional mechanism with H₂ addition as the rate‐limiting step.     

Catalyst Activity and Selectivity in the Isomerising Alkoxycarbonylation of Methyl Oleate

The synthesis of unsymmetrical diphosphine ligands ( 3 a – g ) with an o‐tolyl backbone and tert‐butyl, adamantyl, cyclohexyl and isopropyl substituents on the phosphorus moiety is described (1,2‐(CH₂PR₂)(PR′₂)C₆H₄; 3 a : R=tBu, R′=tBu, 3 b : R=tBu, R′=Cy, 3 c : R=tBu, R′=iPr, 3 d : R=Ad, R′=tBu, 3 e : R=Ad, R′=Cy, 3 f : R=Cy, R′=Cy, 3 g : R=Ad, R′=Ad). The corresponding diphosphine–Pd^II ditriflate complexes [(P^P)Pd(OTf)₂] ( 5 a – g ) were prepared and structurally characterised by X‐ray crystallography. These new complexes were studied as catalyst precursors in the isomerising methoxycarbonylation of methyl oleate, and were found to convert methyl oleate into the corresponding linear α,ω‐diester ( L ) with 70–80 % selectivity. The products of this catalytic reaction with the known [{1,2‐(tBu₂PCH₂)₂C₆H₄}Pd(OTf)₂] complex ( 5 h ) were fully analysed, and revealed the formation of the linear α,ω‐diester ( L , 89.0 %), the methyl‐branched diester B1 (4.3 %), the ethyl‐branched diester B2 (1.0 %), the propyl‐branched diester B3 (0.6 %) and all diesters from butyl‐ to hexadecyl‐branched diesters B4 – B16 (overall 4.8 %) at 90 °C and 20 bar CO. The productivity of the catalytic conversion of methyl oleate with complexes 5 a – g varied with the steric bulk of the alkyl substituent on the phosphorus. Ligands with more bulky groups, like tert ‐ butyl or adamantyl (e.g., 5 a , 5 d , 5 g ), were more productive systems. The formation of the catalytically active hydride species [(P^P)Pd(H)(MeOH)]⁺ ( 6‐MeOH ) was investigated and observed directly for complexes 5 a – e and 5 g , respectively. These hydride species were isolated as the corresponding triphenylphosphine complexes ( 6‐PPh₃ ) and fully characterised, including by X‐ray crystallography. The catalytic productivity of 6 a‐PPh₃ was virtually identical to that of 5 a , thereby confirming the efficient hydride formation of 5 a under catalytic conditions.     

Hydrogenation of Imines Catalyzed by Trisphosphine‐Substituted Molybdenum and Tungsten Nitrosyl Hydrides and Co‐Catalytic Acid

Hydride complexes Mo,W(CO)(NO)H(mer‐etpⁱp) (iPr₂PCH₂CH₂)₂PPh=etpⁱp) ( 2 a,b(syn) , syn and anti of NO and Ph(etpⁱp) orientions) were prepared and probed in imine hydrogenations together with co‐catalytic [H(Et₂O)₂][B(C₆F₅)₄] (140 °C, 60 bar H₂). 2 a,b(syn) were obtained via reduction of syn/anti‐Mo,W(NO)Cl₃(mer‐etpⁱp) and syn,anti‐Mo,W(NO)(CO)Cl(mer‐etpⁱp). [H(Et₂O)₂][B(C₆F₅)₄] in THF converted the hydrides into THF complexes syn‐[Mo,W(NO)(CO)(etpⁱp)(THF)][B(C₆F₅)₄]. Combinations of the p‐substituents of aryl imines p‐R¹C₆H₄CH=N‐p‐C₆H₄R² (R¹,R²=H,F,Cl,OMe,α‐Np) were hydrogenated to amines (maximum initial TOFs of 1960 h^?1 ( 2 a(syn) ) and 740 h^?1 ( 2 b(syn) ) for N‐(4‐methoxybenzylidene)aniline). An ‘ionic hydrogenation’ mechanism based on linear Hammett plots (ρ=?10.5, p‐substitution on the C‐side and ρ=0.86, p‐substitution on the N‐side), iminium intermediates, linear P(H₂) dependence, and DKIE=1.38 is proposed. Heterolytic splitting of H₂ followed by ‘proton before hydride’ transfers are the steps in the ionic mechanism where H₂ ligand addition is rate limiting.