In Search of Fulminate Analogues: L_nM≡CP=NR

Abstract

The “CPNR” ligand may be viewed as being isolobal with fulminate, CNO; however, attempts to prepare a complex of such a ligand resulted instead in a range of novel imino and aminophosphinocarbyne complexes. Sequential treatment of [Mo(≡CBr)(CO)2(Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) with nBuLi and ClP=NMes* (Mes*=C6H2tBu3‐2,4,6) afforded mixtures of the complexes [Mo(≡CPnBuNHMes*)(CO)2(Tp*)] and traces of the bimetallic products [Mo2{μ2‐C2P2O(NHMes)2}(CO)4(Tp*)2] and [Mo2(μ2‐C2PNHMes)(CO)4(Tp*)2]. The reaction of [W(≡CBr)(CO)2(Tp*)] with nBuLi and ClP=NMes* afforded predominantly the mononuclear carbyne [W{≡CP(=NMes*)nBu2})(CO)2(Tp*)] and traces of the binuclear complex [W2(μ‐C2PNHMes)(CO)4(Tp*)2] which is also obtained when tBuLi is used. Although not isolable, the intended complexes [M(≡CPNMes*)(CO)2(Tp*)] could be generated in situ and spectroscopically characterized via the reactions of the stannyl carbynes [M(≡CSnnBu3)(CO)2(Tp*)] and ClP=NMes*. The preceding observations are mechanistically interpreted with reference to a computational interrogation of the model complex [Mo(≡CP=NCH3)(CO)2(Tp*)], the LUMO of which has considerable phosphorus character.

Pnictogen‐Functionalised C1 Ligands: MC‐ARn (n=0, 1, 2, 3)

“…These could not, however, be isolated as pure complexes as they were found to rapidly discolour to orange‐brown mixtures of products even at low temperatures (Scheme 8). Several of these subsequent products were isolated in low yields and, whilst consistent with the formation of iminophosphanylcarbynes, highlight shortcomings of the lithiocarbyne protocols en route to species that retain a high degree of reactivity [31] …”

“…[30] With an additional equivalent of lithiocarbyne 6b (or if only half an equivalent of PCl 2 NR 2 is initially employed)t he aminobis(alkylidynyl)phosphines [W 2 (m 2 -C 2 PNR 2 )(CO) 4 (Tp*) 2 ]( R= Et 25 a, iPr 25 b)a re obtained. [30,31] Treatment of 23 b with Li[HBEt 3 ]a llowed ar are example of as econdary aminophosphine, [W{ CPH(NiPr 2 )}(CO) 2 (Tp*)],t ob es pectroscopically observed althoughi tw as formed amongst many other products,o fw hich only 24 b could be identified (Li[Et 3 BH] unusually serving as a nucleophilic ethylating agent). Generally,s uch speciesa re thermally unstable towards amine elimination and cyclo-polyphosphine formation;t he exaggerateds teric bulk of the 'W(CO) 2 (Tp*)' unit presumably arrests this process and imparts am odicum of kinetic stability.…”

“…highlight shortcomings of the lithiocarbyne protocols en route to speciest hat retain ah igh degree of reactivity. [31] In the case of the molybdenumc omplex 28 a,i ti st hought that adventitious nBuLi, from the initial lithium-halogen exchange required to prepare 6a in situ, reacts at phosphorus and, followingc hromatographic workup,f urnishes the aminophosphinocarbyne [Mo{ CP(nBu) [31] These results suggest that elusive iminophosphanylcarbynes appear viable,b ut that the high phosphorus-centred reactivity has so far prevented their isolation under the conditions of their generation. Computational interrogation of the model compound [Mo(CPNMe)(CO) 2 (Tp*)] found that bending occurs at both Pa nd N. The LUMO, located on the MoCPN spine,h as substantial contribution from phosphorus, consistent with the P-regioselectivity of nucleophilic attack.…”

“…Generally,s uch speciesa re thermally unstable towards amine elimination and cyclo-polyphosphine formation;t he exaggerateds teric bulk of the 'W(CO) 2 (Tp*)' unit presumably arrests this process and imparts am odicum of kinetic stability. [30] Treatment of 23 b with Al 2 Cl 6 or Ga 2 Cl 6 results in the appearance of new 31 PNMR peaks, shifteds ubstantially to higherf requencyf rom d P = 129.4 in 23 b to d P = 283.5 and 294.6, respectively,c onsistent with reduced coordination at phosphorus and formation of the desired phosphenium cation [W(CPNiPr 2 )(CO) 2 (Tp*)] + [26] + rather than simpleP !Al/Ga or P-Cl!Al/Ga Lewis adduct formation( Scheme 7). These reactions did not proceed cleanly and no pure product could be obtained;h owever, when the chloride abstraction was performed in the presence of diphenylacetylene, the similarly intractable phosphirenium carbyne [W{ CP(CPhCPh)NiPr 2 }(CO) 2 (Tp*)] + ([27] + )w as presumably formed based on spectroscopicd ata, whichw as consistent with other phosphireniums (d P = À77.9, 2 J WP = 221 Hz).…”

Phosphorus and Arsenic Atom Transfer to Isocyanides to Form π‐Backbonding Cyanophosphide and Cyanoarsenide Titanium Complexes

“…TheO CP À ligand in 4 remains unscathed under both photolysis-and thermolysis conditions (full spectrum from aX el amp,1h; 60 8 8C, 2h), highlighting the unique role of the reducing Ti II ion in assembling the cyanophosphide ligand in 3 P .Hill reported an alternative route to the isomeric {CPN} unit, relying on expulsion of LiCl from ClP = N(2,4,6-t Bu 3 C 6 H 2 )a nd Mo/W lithiocarbynes. [22] As judged from IR spectroscopy,t he divergent reactivity of 2 Ti and 2 V aligns with their relative degree of isocyanide activation and mode of coordination to OCP À :T he C Ns tretching frequency of 2 Ti is redshifted (2096 cm À1 ), whereas that of 2 V is blueshifted (2160 cm À1 ) from free AdNC (2124 cm À1 ). Thea vid reactivity of OCP À toward 2 Ti compared to its more inert reactivity toward 2 V may even be general in that we previously observed OCP À to reductively decarbonylate upon association with [(nacnac)TiCl(OAr)],w hereas the analogous reaction for V III afforded am etastable [(nacnac)V(PCO)(OAr)] (nacnac À = CH{(CH 3 )CNAr} 2 ;A r = 2,6-i Pr 2 C 6 H 3 ).…”