Miguel A. Casado

Direct Access to Parent Amido Complexes of Rhodium and Iridium through NH Activation of Ammonia

Financial support from CONSOLIDER INGENIO-2010 program under the projects MULTICAT (CSD2009-00050) and Factoria de Cristalizacion (CSD2006-0015). P.G.O. acknowledges financial support from the CSIC “JAE-Doc” program.

Terminal and bridging parent amido 1,5-cyclooctadiene complexes of rhodium and iridium.

The ready availability of rare parent amido d(8) complexes of the type [{M(μ-NH2)(cod)}2] (M=Rh (1), Ir (2); cod=1,5-cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di-olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(μ-NH2)(CO)2}2 ] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH2Cl2 or CHCl3, giving the diiridium(II) products [(Cl)(cod)Ir(μ-NH2)2Ir(cod)(R)] (R=CH2Cl or CHCl2) as a result of a two-center oxidative addition and concomitant metal-metal bond formation. However, reaction with ClCH2CH2Cl afforded the symmetrical adduct [{Ir(μ-NH2)(Cl)(cod)}2] upon release of ethylene. We found that the rhodium complex 1 exchanged the di-olefines stepwise upon addition of selected phosphanes (PPh3, PMePh2, PMe2Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(μ-NH2)2Rh(PR3)2], and finally the isolation of the respective tetraphosphanes [{Rh(μ-NH2)(PR3)2}2]. On the other hand, the iridium complex 2 reacted with PMe2 Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH2)(PMePh2)2]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh2)2]. The heterocyclic carbene IPr (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) also split the amido bridges in complexes 1 and 2, allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH2)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs2CO3, finding that the iridium complex 2 is more active than the rhodium analogue 1.

The dehydrogenation of alcohols through a concerted bimetallic mechanism involving an amido-bridged diiridium complex

Financial support from the CONSOLIDER INGENIO-2010 program under the projects MULTICAT (CSD2009-00050) and Factoria de Cristalizacion (CSD2006-0015), and the DGA-ESF are acknowledged. P.G.O. acknowledges financial support from the CSIC “JAE-Doc” program, a contract co-funded by the ESF.

Early (Ti, Zr)-late (Rh, Ir) heteronuclear complexes with bridging sulphido ligands

Abstract We report in this account on the controlled synthesis of novel d 0 –d 8 early-late heteropolynuclear diolefin and carbonyl clusters. The synthetic approach was based on additive–deprotonation reactions involving the titanium and zirconium bis-hydrosulphido complexes of formula [Cp 2 Ti(SH) 2 ] and [Cp tt 2 Zr(SH) 2 ] and appropriate rhodium and iridium diolefin and carbonyl compounds. The significant differences between the resulting early-late complexes and their structures coming from the titanium or zirconium metalloligand precursors are highlighted. The catalytic activity of some representative titanium–rhodium and zirconium–rhodium compounds towards alkene hydroformylation was explored. Interestingly, the heterotetranuclear ‘CpTi(μ 3 -S) 3 Rh 3 ’ structure was maintained as such under mild conditions. To cite this article: L.A. Oro et al., C. R. Chimie 6 (2003) 000–000 .

C-NH2 bond formation mediated by iridium complexes.

In the presence of phosphanes (PR3 ), the amido-bridged trinuclear complex [{Ir(μ-NH2 )(tfbb)}3 ] (tfbb=tetrafluorobenzobarrelene) transforms into mononuclear discrete compounds [Ir(1,2-η(2) -4-κ-C12 H8 F4 N)(PR3 )3 ], which are the products of the CN coupling between the amido moiety and a vinylic carbon of the diolefin. An alternative synthetic approach to these species involves the reaction of the 18 e(-) complex [Ir(Cl)(tfbb)(PMePh2 )2 ] with gaseous ammonia and additional phosphane. DFT studies show that both transformations occur through nucleophilic attack. In the first case the amido moiety attacks a diolefin coordinated to a neighboring molecule following a bimolecular mechanism induced by the highly basic NH2 moiety; the second pathway involves a direct nucleophilic attack of ammonia to a coordinated tfbb molecule.

Nucleophilicity and P-C bond formation reactions of a terminal phosphanido iridium complex

The diiridium complex [{Ir(ABPN2)(CO)}2(μ-CO)] (1; [ABPN2](-) = [(allyl)B(Pz)2(CH2PPh2)](-)) reacts with diphenylphosphane affording [Ir(ABPN2)(CO)(H) (PPh2)] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the terminal phosphanido lone pair to the HOMO of 2, indicating nucleophilic character of this ligand, which is evidenced by reactions of 2 with typical electrophiles such as H(+), Me(+), and O2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir(ABPN2)(CO)(H)(PPh2CH2CO2Me)][PF6] ([6]PF6) or [Ir(ABPN2)(CO)(Cl)(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving P-C bond formation, depending on the reaction conditions. New complexes having iridacyclophosphapentenone and iridacyclophosphapentanone moieties result from reactions of 2 with dimethyl acetylenedicarboxylate and dimethyl maleate, respectively, as a consequence of a further incorporation of the carbonyl ligand. In this line, the terminal alkyne methyl propiolate gave a mixture of a similar iridacyclophosphapentanone complex and [Ir(ABPN2){CH═C(CO2Me)-CO}{PPh2-CH═CH(CO2Me)}] (10), which bears the functionalized phosphane PPh2-CH═CH(CO2Me) and an iridacyclobutenone fragment. Related model reactions aimed to confirm mechanistic proposals are also studied.

Peripheral SH-functionalisation of carbosilane dendrimers including the synthesis of the model compound dimethylbis(propanethiol)silane and their interaction with rhodium complexes

Treatment of the allyl-containing compounds Me2Si(CH2CHCH2)2 and MeSi(CH2CHCH2)3 with thioacetic acid in the presence of AIBN gave Me2Si[(CH2)3SC(O)CH3]2 and MeSi[(CH2)3SC(O)CH3]3, respectively, which were reduced with LiAlH4 to the dithiols Me2Si[(CH2)3SH]2(3) and MeSi[(CH2)3SH]3(4). This protocol was applied to the first and second generations of the doubly and triply-branched carbosilane allyl dendrimers, Si[(CH2)3SiMe(CH2CHCH2)2]4(G(1)allyl-8), Si[(CH2)3SiMe{(CH2)3SiMe(CH2CHCH2)2}2]4(G(2)allyl-16), Si[(CH2)3Si(CH2CHCH2)3]4(G(1)allyl-12), and Si[(CH2)3Si{(CH2)3Si(CH2CHCH2)3}3]4(G(2)allyl-36) to give the corresponding SH functionalised surface dendrimers Si[(CH2)3SiMe(CH2CH2CH2SH)2]4(G(1)SH-8), G(2)SH-16, G(1)SH-12, and G(2)SH-36. Reactions of 3 with [M(acac)(diolefin)](M = Rh, Ir; diolefin = 1,5-cyclooctadiene, 2,5-norbornadiene) gave the compounds of the type [M2(mu-Me2Si[(CH2)3S]2)(diolefin)2]n. These diolefin complexes are octanuclear (n= 4) in solution while the complex [Rh2(mu-Me2Si[(CH2)3S]2)(cod)2]n(5) is tetranuclear in the solid state. The structure of 5, solved by X-ray diffraction methods, consists of a 20-membered metallomacrocycle formed by two dimethylbis(propylthiolate)silane moieties bridging four fragments Rh(cod) in a mu2 fashion through the sulfur atoms. Treatment of [Rh(acac)(CO)2] with 3 gave [Rh2(mu-Me2Si[(CH2)3S]2)(CO)4]n, which is a mixture of tetra (n= 2) and octanuclear (n= 4) complexes in a 2 : 1 ratio in solution, while the related complex [Rh2(mu-Me2Si[(CH2)3S]2)(CO)2(PPh3)2]2 is tetranuclear. Reactions of [Rh(acac)(L-L)](L-L = cod, (CO)2, (CO)(PPh3)) with 4 and the dendrimers G(1)SH-8, G(2)SH-16, and G(1)SH-12, gave microcrystalline solids of formulae [Rh3(MeSi[(CH2)3S]3)(L-L)3]n, [Si[(CH2)3SiMe{(CH2)3SRh(cod)}2]4]n([G(1)Rh(cod)-8]n), [Si[(CH2)3Si{(CH2)3SRh(cod)}3]4]n([G(1)Rh(cod)-12]n), etc., which presumably are tridimensional coordination polymers.

Tris(pyrazolyl)borate carbosilane dendrimers and metallodendrimers

A modified tris(pyrazolylborate) ligand has been prepared in two steps. First, reaction of triisopropylborate with allylmagnesium bromide and further treatment with benzoyl chloride gave CH(2) = CHCH(2)B(O(i)Pr), which was then reacted with potassium pyrazolate and pyrazole to give the compound K[CH(2) = CHCH(2)Bpz(3)]. The new allyl-containing scorpionate anion of acts as a bi- or tri-dentate ligand, as shown by the mononuclear complexes [CH(2) = CHCH(2)Bpz(3)M(LL)] (M = Rh, LL = nbd, ; LL = tfb, ; LL = (CO)(PPh(3)), ; M = Ir, LL = cod, ), obtained from reactions of the chlorido-bridged dinuclear complexes [{M(mu-Cl)(LL)}(2)] with 2. Furthermore, the borate represents a key material to achieve the attachment of tris(pyrazolyl)borate groups to the peripheries of carbosilane dendrimers. Thus, the platinum-catalyzed hydrosilylation reactions of compound with the dendritic cores Si[(CH(2))(3)SiMe(2)H](4) (G(0)-(SiH)(4)), (G(1)-(SiH)(8)), and (G(2)-(SiH)(16)) gave the corresponding borate-containing dendrimers Si[(CH(2))(3)SiMe(2)(CH(2))(3)B(O(i)Pr)(2)](4) (G(0)-B(4)), Si[(CH(2))(3)SiMe{(CH(2))(3)SiMe(2)(CH(2))(3)B(O(i)Pr)(2)}(2)](4) (G(1)-B(8)), and Si[(CH(2))(3)SiMe{(CH(2))(3)SiMe[(CH(2))(3)SiMe(2)(CH(2))(3)B(O(i)Pr)(2)](2)}(2)](4) (G(2)-B(16)) selectively in the anti-Markovnikov direction. Further reactions of G(0)-B(4), G(1)-B(8) and G(2)-B(16) with potassium pyrazolate and pyrazole rendered the corresponding polyanionic dendrimers K(4)[Si{(CH(2))(3)SiMe(2)(CH(2))(3)Bpz(3)}(4)] (G(0)-(Bpz(3))(4)), G(1)-(Bpz(3))(8), and G(2)-(Bpz(3))(16), respectively, which contain 4, 8, and 16 tris(pyrazolyl)borate groups symmetrically located around the dendritic peripheries. These unusual polyanionic dendrimers are excellent scaffolds to support metal centres, as shown by the reactions of G(0)-(Bpz(3))(4), G(1)-(Bpz(3))(8), and G(2)-(Bpz(3))(16) with [{Rh(mu-Cl)(nbd)}(2)] to give the neutral rhodadendrimers [Si{(CH(2))(3)SiMe(2)(CH(2))(3)Bpz(3)Rh(nbd)}(4)] G(0)-(Bpz(3)Rh)(4), G(1)-(Bpz(3)Rh)(8) and G(2)-(Bpz(3)Rh)(16) as stable solids in excellent yields. Following this protocol, mixed rhodium/iridium metallodendrimers can be prepared.

Rhodium?tetranuclear complexes as building blocks for the construction of coordination polymers: chiroselectivity in the formation of [ClCuRh4(µ-PyS2)2(cod)4]n (H2PyS2 = 2,6-dimercaptopyridine)

The reaction of the complex [Rh4(µ-PyS2)2(cod)4], containing two juxtaposed coordination donor sites, with CuCl creates the coordination polymer [ClCuRh4(µ-PyS2)2(cod)4]n. This polymeric structure results from the self-assembly of alternating rhodium tetranuclear complexes and CuCl as linking units, and shows zigzag chains containing exclusively homochiral tetranuclear building blocks

CCDC 1538222: Experimental Crystal Structure Determination

Related Article: Inmaculada Mena, Pilar Garcia-Orduna, Victor Polo, Fernando J. Lahoz, Miguel A. Casado, Luis A. Oro||Dalton Trans.|||doi:10.1039/C7DT01924F