Protonolysis of an α‑Hydroxyl Ligand for the Generation of a PC_carbeneP Pincer Complex and Subsequent Reactivity Studies

A rhodium α-hydroxylalkyl complex (<b>1</b>) reacts rapidly with Brookhart’s acid, [H­(OEt₂)₂]­[B­(3,5-(CF₃)₂-C₆H₃)₄], to generate a cationic PC_carbeneP complex (<b>2</b>). Complex <b>2</b> can also be accessed from salt metathesis of an α-hydroxyalkyl hydrochlorido rhodium­(III) complex (<b>4</b>) with Na­[B­(3,5-(CF₃)₂-C₆H₃)₄]. The reactivity of compound <b>2</b> is explored through a series of reactions with various nucleophilic and electrophilic reagents

Mechanistic Studies on the Copper-Catalyzed N‑Arylation of Alkylamines Promoted by Organic Soluble Ionic Bases

Experimental studies on the mechanism of copper-catalyzed amination of aryl halides have been undertaken for the coupling of piperidine with iodobenzene using a Cu­(I) catalyst and the organic base tetrabutylphosphonium malonate (TBPM). The use of TBPM led to high reactivity and high conversion rates in the coupling reaction, as well as obviating any mass transfer effects. The often commonly employed O,O-chelating ligand 2-acetylcyclohexanone was surprisingly found to have a negligible effect on the reaction rate, and on the basis of NMR, calorimetric, and kinetic modeling studies, the malonate dianion in TBPM is instead postulated to act as an ancillary ligand in this system. Kinetic profiling using reaction progress kinetic analysis (RPKA) methods show the reaction rate to have a dependence on all of the reaction components in the concentration range studied, with first-order kinetics with respect to [amine], [aryl halide], and [Cu]_total. Unexpectedly, negative first-order kinetics in [TBPM] was observed. This negative rate dependence in [TBPM] can be explained by the formation of an off-cycle copper­(I) dimalonate species, which is also argued to undergo disproportionation and is thus responsible for catalyst deactivation. The key role of the amine in minimizing catalyst deactivation is also highlighted by the kinetic studies. An examination of the aryl halide activation mechanism using radical probes was undertaken, which is consistent with an oxidative addition pathway. On the basis of these findings, a more detailed mechanistic cycle for the C–N coupling is proposed, including catalyst deactivation pathways

Convergent (De)Hydrogenative Pathways via a Rhodium α‑Hydroxylalkyl Complex

We report the convergent reaction pathways between [RhH­(PPh₃)₄] and POP ketone (<b>1</b>) and alcohol (<b>2</b>) ligands that terminate in the formation of an α-hydroxylalkyl rhodium­(I) complex (<b>3</b>), representing two halves of a formal reduction/oxidation pathway between <b>1</b> and <b>2</b>. In the case of hydride transfer to <b>1</b>, the formation of the α-hydroxylalkyl rhodium­(I) complex (<b>3</b>) proceeds via a rare hydrido­(η²-carbonyl) complex (<b>4</b>). C–H activation in <b>2</b> at the proligand’s central methine position, rather than O–H activation of the hydroxy motif, followed by loss of dihydrogen also generates the α-hydroxylalkyl rhodium­(I) complex (<b>3</b>). The validity of the postulated reaction pathways is probed with DFT calculations. The observed reactivity supports α-hydroxylalkyl complexes as competent intermediates in ketone hydrogenation catalyzed by rhodium hydrides and suggest that ligands <b>1</b> and <b>2</b> may be “noninnocent” coligands in reported hydrogenation catalyst systems in which they are utilized

Multimetallic Complexes and Functionalized Gold Nanoparticles Based on a Combination of d- and f‑Elements

The new DO3A-derived dithiocarbamate ligand, DO3A-^tBu-CS₂K, is formed by treatment of the ammonium salt [DO3A-^tBu]­HBr with K₂CO₃ and carbon disulfide. DO3A-^tBu-CS₂K reacts with the ruthenium complexes <i>cis</i>-[RuCl₂(dppm)₂] and [Ru­(CHCHC₆H₄Me-4)­Cl­(CO)­(BTD)­(PPh₃)₂] (BTD = 2,1,3-benzothiadiazole) to yield [Ru­(S₂C-DO3A-^tBu)­(dppm)₂]⁺ and [Ru­(CHCHC₆H₄Me-4)­(S₂C-DO3A-^tBu)­(CO)­(PPh₃)₂], respectively. Similarly, the group 10 metal complexes [Pd­(<i>C,N</i>-C₆H₄CH₂NMe₂)­Cl]₂ and [PtCl₂(PPh₃)₂] form the dithiocarbamate compounds, [Pd­(<i>C,N</i>-C₆H₄CH₂NMe₂)­(S₂C-DO3A-^tBu)] and [Pt­(S₂C-DO3A-^tBu)­(PPh₃)₂]⁺, under the same conditions. The linear gold complexes [Au­(S₂C-DO3A-^tBu)­(PR₃)] are formed by reaction of [AuCl­(PR₃)] (R = Ph, Cy) with DO3A-^tBu-CS₂K. However, on reaction with [AuCl­(tht)] (tht = tetrahydrothiophene), the homoleptic digold complex [Au­(S₂C-DO3A-^tBu)]₂ is formed. Further homoleptic examples, [M­(S₂C-DO3A-^tBu)₂] (M = Ni, Cu) and [Co­(S₂C-DO3A-^tBu)₃], are formed from treatment of NiCl₂·6H₂O, Cu­(OAc)₂, or Co­(OAc)₂, respectively, with DO3A-^tBu-CS₂K. The molecular structure of [Ni­(S₂C-DO3A-^tBu)₂] was determined crystallographically. The <i>tert</i>-butyl ester protecting groups of [M­(S₂C-DO3A-^tBu)₂] (M = Ni, Cu) and [Co­(S₂C-DO3A-^tBu)₃] are cleaved by trifluoroacetic acid to afford the carboxylic acid products, [M­(S₂C-DO3A)₂] (M = Ni, Cu) and [Co­(S₂C-DO3A)₃]. Complexation with Gd­(III) salts yields trimetallic [M­(S₂C-DO3A-Gd)₂] (M = Ni, Cu) and tetrametallic [Co­(S₂C-DO3A-Gd)₃], with <i>r</i>¹ values of 11.5 (Co) and 11.0 (Cu) mM^–1 s^–1 per Gd center. DO3A-^tBu-CS₂K can also be used to prepare gold nanoparticles, Au@S₂C-DO3A-^tBu, by displacement of the surface units from citrate-stabilized nanoparticles. This material can be transformed into the carboxylic acid derivative Au@S₂C-DO3A by treatment with trifluoroacetic acid. Complexation with Gd­(OTf)₃ or GdCl₃ affords Au@S₂C-DO3A-Gd with an <i>r</i>¹ value of 4.7 mM^–1 s^–1 per chelate and 1500 mM^–1 s^–1 per object