Hydrophosphination-type reactivity promoted by bismuth phosphanides: scope and limitations

Recent advances in catalytic pnictogen bond forming reactions via dehydrocoupling and hydrofunctionalization

An examination of several catalytic reactions among the group 15 elements is presented. The connections between the chemistry of the pnictogens can sometimes be challenging, but aspects of metal-pnictogen reactivity are the key. The connecting reactivity comes from metal-catalyzed transformations such as dehydrocoupling and hydrofunctionalization. Pivotal mechanistic insights from E-N heterodehydrocoupling have informed the development of highly active catalysts for these reactions. Metal-amido nucleophilicity is often at the core of this reactivity, which diverges from phosphine and arsine dehydrocoupling. Nucleophilicity connects to the earliest understanding of hydrophosphination catalysis, but more recent catalysts are leveraging enhanced insertion activity through photolysis. This photocatalysis extends to hydroarsination, which may also have more metal-arsenido nucleophilicity than anticipated. However, metal-catalyzed arsinidene chemistry foreshadowed related phosphinidene chemistry by years. This examination shows the potential for greater influence of individual discoveries and understanding to leverage new advances between these elements, and it also suggests that the chemistry of heavier elements may have more influence on what is possible with lighter elements.

Reactivity of a Cationic Bismuth Amide towards Unsymmetric Heterocumulenes

The reactivity of a literature-known, ring-strained bismuth amide cation towards a range of unsymmetric heterocumulene substrates has been investigated. Reactions with ketenes R₂ C=C=O (R=Me, Ph), isocyanates R'N=C=O, and isothiocyanates R'N=C=S (R'=Ph, 4-CF₃ -C₆ H₄ ) proceed via facile insertion of the heterocumulene in the Bi-N bond of the cationic bismuth amide. Unexpectedly pronounced differences in the regioselectivity of these insertion reactions have been observed, yielding a rich variety of heterocycle motifs (BiC₂ NC₂ , BiC₂ NCO, BiC₂ NCS, BiC₂ NCN), some of which are unprecedented. Parameters that control the regioselectivity of the insertion reactions have been identified and are discussed based on experimental and theoretical investigations. Analytical techniques applied in this work include heteronuclear and two-dimensional NMR spectroscopy, IR spectroscopy, elemental analysis, single-crystal X-ray diffraction analyses, and DFT calculations.

Heavy Chains: Synthesis, Reactivity and Decomposition of Interpnictogen Chains with Terminal Diaryl Bismuth Fragments

In this work, we report the preparation of multiple interpnictogen chain compounds with three consecutive pnictogen atoms and terminal Ar₂ Bi fragments (Ar=Ph, Mes). Symmetrical compounds of the form Ar₂ Bi-E(tBu)-Bi₂ Ar (1: Ar=Ph, E=P; 2: Ar=Ph, Mes, E=As) as well as ternary interpnictogen compounds of the form Ar₂ Bi-E¹ (tBu)-E² tBu₂ (Ar=Ph, Mes; 4: E¹ =P, E² =As; 5: E¹ =P, E² =Sb; 6: E¹ =As, E² =P) were prepared. The decomposition in solution at room temperature and under the influence of light was studied for compounds 1-6. The reactivity of 1_Ph and 2_Ph with the small N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene (Me₂ IMe) was also studied. In the case of 1_Ph , the formation and consecutive decomposition of Me₂ IMe=PtBu (8) was observed in solution. Hence, it was shown that 1_Ph can react as a "masked phosphinidene". In the case of 2_Ph , no reaction with Me₂ IMe was observed. All isolated compounds were analysed by NMR and IR spectroscopy, mass spectrometry, elemental analysis and single-crystal X-ray diffraction.

Broken Promises? On the Continued Challenges Faced in Catalytic Hydrophosphination

In this Perspective, we discuss what we perceive to be the continued challenges faced in catalytic hydrophosphination chemistry. Currently the literature is dominated by catalysts, many of which are highly effective, that generate the same phosphorus architectures, e.g., anti-Markovnikov products from the reaction of activated alkenes and alkynes with diarylphosphines. We highlight the state of the art in stereoselective hydrophosphination and the scope and limitations of chemoselective hydrophosphination with primary phosphines and PH₃. We also highlight the progress in the chemistry of the heavier homologues. In general, we have tried to emphasize what is missing from our hydrophosphination armament, with the aim of guiding future research targets.

Novel ferrocenyl functionalised phosphinecarboxamides: synthesis, characterisation and coordination

The synthesis of two novel ferrocenyl-substituted phosphinecarboxamides, FcNHC(O)PH₂ (1; Fc = ferrocenyl) and FcCH₂NHC(O)PH₂ (2), is reported. These two primary phosphines were obtained by the reaction of aminoferrocene with sodium 2-phosphaethynolate in the presence of a proton source or, directly, from aminomethylferrocene hydrochloride and sodium 2-phosphaethynolate. Their ability to act as ligands was probed via reactions of 1 with rhodium(iii) and ruthenium(ii) precursors. The isoelectronic metal complexes [(η⁵-C₅Me₅)RhCl₂(1-κP)] and [(η⁶-mes)RuCl₂(1-κP)] were obtained. Treatment of these compounds with a base resulted in HCl elimination to afford phosphide-bridged dirhodium and diruthenium complexes highlighting that on coordination to a metal, the P-H bonds of these phosphinecarboxamides become increasingly protic.

The first ring-expanded NHC–copper(i) phosphides as catalysts in the highly selective hydrophosphination of isocyanates

The first copper(i) phosphides supported by ring-expanded N-heterocyclic carbenes have been synthesised and react readily with heterocumulenes. These copper(i) phosphides are highly active and selective in the hydrophosphination of isocyanates.

Distibanes and Distibenes from Reduction of Sb(NONR )Cl by using MgI Reagents

The bis(amidodimethyl)disiloxane antimony chlorides Sb(NON^R )Cl (NON^R =[O(SiMe₂ NR)₂ ]^2- ; R=tBu, Ph, 2,6-Me₂ C₆ H₃ =Dmp, 2,6-iPr₂ C₆ H₃ =Dipp, 2,6-(CHPh₂ )₂ -4-tBuC₆ H₂ =tBu-Bhp) are reduced to Sb^II and Sb^I species by using Mg^I reagents, [Mg(BDI^R' )]₂ (BDI=[HC{C(Me)NR'}₂ ]^- ; R'=2,4,6-Me₃ C₆ H₂ =Mes, Dipp). Stoichiometric reactions with Sb(NON^R )Cl (R=tBu, Ph) form dimeric Sb^II stibanes [Sb(NON^R )]₂ , shown crystallographically to contain Sb-Sb single bonds. The analogous distibane with R=Dmp substituents has an exceptionally long Sb-Sb interaction and exhibits spectroscopic and reactivity properties consistent with radical character in solution. When R=Dipp, reductions with Mg^I reagents directly give distibenes [Sb(μ-NON^Dipp )Mg(BDI^R' )(THF)_n ]₂ (R'=Mes, n=1; R'=Dipp, n=0). Crystallographic analysis shows a trans-substitution of the Sb=Sb double bond, with bridging NON^Dipp -ligands between the Sb^I and Mg^II centres. An attempt to access the NON^Ph -analogue using the same protocol afforded the polystibide cluster Sb₈ [μ₄ ,η^2:2:2:2 -Mg(BDI^Mes )]₄ , which co-crystallized with the ligand transfer product, [Mg(BDI^Mes )]₂ (μ-NON^Ph ).

A study of di(amino)stibines with terminal Sb(iii) hydrogen-ligands by X-ray- and neutron-diffraction

The bis(amidodimethyl)disiloxane ligands [O{SiMe2NR}2]2- (R = 2,6-Me2C6H3 (Ar') and 2,6-iPr2C6H3 (Ar), abbreviated [NONR]2-, are a stable support for Sb(iii) complexes of general formula Sb(NONR)X (X = Cl, H). The compounds are monomeric in the solid-state, with bidentate N,N'-coordination of the [NONR]2- and terminal chloride/hydrogen-ligands. Sb(NONAr')H was analyzed by single-crystal neutron diffraction, giving the first accurate parameters for the Sb-H bond to an antimony(iii) centre.