A Scandium‐Stabilized Diisophosphaethynolate Ligand: [OCPPCO]⁴⁻

Abstract

The first example of the OCPPCO ligand, diisophosphaethynolate, is reported via reductive coupling of a Sc-OCP precursor. Upon reduction with KC , isolation of the dinuclear complex, namely [K(OEt )] [(nacnac)Sc(OAr)] (OCPPCO), is observed, leading to a unique motif [OCPPCO] , stabilized by two scandium centers. Detailed NMR spectra of all complexes as well as IR and single crystal X-ray studies were obtained to fully elucidate the nature of these complexes in solution as well as in the solid state. Theory is combined to probe the electronic structure and orbitals responsible for the bonding interactions in the Sc-OCPPCO-Sc skeleton but also to compare to the linear mode observed in the precursor.

The Chemistry of the 2‐Phosphaethynolate Anion

“…[18] In principle,such reductions may be used as amethod of cleaving the OÀCbond to generate the cyaphide ion (C P À )a nd an oxide (O 2À ), ar eactivity mode that has been explored recently (see Section 5.3). Ther eductive dimerization of the OCP À anion to afford the formally tetraanionic species (OCPPCO) 4À has recently been achieved in the coordination sphere of scandium, by reduction of ap hosphaethynolate-scandium(III) compound with potassium graphite.…”

“…TheE ÀPÀCb ond angles for the majority of phosphaketenyl compounds approach 908 8 (for example,9 4.7(1)8 8 for [W-(CO) 5 (PCO)] À ), which can be rationalized by taking into consideration the frontier molecular orbitals of OCP À .T he HOMO of this anion has asignificant degree of phosphorus porbital character, implying that on coordination to aL ewis acid it acts as atwo-electron s-donor, but through apolarized p-bonding orbital. [34] In these compounds,a nd in the two scandium and uranium compounds that have been isolated since, {CH[N(Dipp)C(CH 3 )] 2 }Sc(ODipp)(THF)(OCP) [18] and [( Ad,Me ArO) 3 N]U(DME)(OCP), the OCP À ion binds through the oxygen atom in al inear fashion with MÀOÀCa ngles approaching 1808 8 (170.9(3)8 8 for (amid) 3 U(OCP)). By contrast, reactions involving metal centres that are more ionic in character favour formation of oxygen-bonded phosphaethynolate compounds (E À O À C P).…”

“…[34] In these compounds,a nd in the two scandium and uranium compounds that have been isolated since, {CH[N(Dipp)C(CH 3 )] 2 }Sc(ODipp)(THF)(OCP) [18] and [( Ad,Me ArO) 3 N]U(DME)(OCP), the OCP À ion binds through the oxygen atom in al inear fashion with MÀOÀCa ngles approaching 1808 8 (170.9(3)8 8 for (amid) 3 U(OCP)). [18] Forthe main-group elements,phosphaketenyl compounds (such as the phosphanyl phosphaketene E pictured in Figure 2) are also quite numerous and have been shown to readily decarbonylate affording phosphandiyls,t he majority of which oligomerise on formation (see below). This allows for subsequent coordination of the formal PC triple bond to other metal centres,a sd emonstrated by the formation of an adduct between (amid) 3 Th(OCP) and aN i-(COD) fragment (where COD = 1,5-cyclooctadiene); [34] or perhaps more remarkably,inthe cleavage of the O À Cbond to afford the cyaphide ligand (C P À )asshown by Meyer and coworkers (see below).…”

A Scandium‐Stabilized Diisophosphaethynolate Ligand: [OCPPCO]4−

“…[7] Theidentity of this white powder was confirmed by 1 HNMR spectroscopy with aconcentrated sample in C 6 D 6 ,featuring resonances assignable for both nacnac and aryloxide ligands,a sw ell as for as ingle Scbound THF ligand. [8] TheT HF ligand in complex 1 is also labile,s ince dilute benzene solutions significantly change the color from translucent to teal presumably by forming (nacnac)ScCl(OAr), whereas addition of THF reverses the process. Despite not being able to obtain single crystals of 1 for as olid-state X-ray diffraction study (XRD), we anticipate this is af ive-coordinate Sc 3+ complex having pseudo-C s symmetry in solution at room temperature based on the NMR spectroscopic data.…”

“…1 HNMR spectroscopic resonances attributable to the backbone methyl groups of the nacnac ligand, as well that of isopropyl methyl and methine groups of the nacnac ligand, suggest that there is symmetry across the ligand due to fluxional behavior in solution. [8] Tr eatment of 1 with NaOCP(dioxane) 2.5 in THF and stirring the reaction overnight at room temperature led to color change from nearly colorless to pale yellow,w ith concurrent formation of aw hite precipitate.W orkup of the reaction mixture and subsequent crystallization at À35 8 8Ci naTHF/hexanes mixture produced pale yellow crystals of (nacnac)Sc(OAr)-(OCP)(THF) (2;Scheme 1) in 43 %yield. [8] TheT HF ligand in complex 1 is also labile,s ince dilute benzene solutions significantly change the color from translucent to teal presumably by forming (nacnac)ScCl(OAr), whereas addition of THF reverses the process.…”