Making the True “CP” Ligand

Abstract

The quest for cyaphide, the phosphorus equivalent of cyanide, has been a continuous struggle for many years. Potential applications arising from the use of C P as a bridging ligand between two metals, the incorporation of CP into coordination polymers and new materials, and the basic synthetic challenges of making C P have provided inspiration for decades. While phosphaalkynes (R À C P) have been known for some time, [1][2][3] the terminal MÀCP has only been reported as a transient species. [4,5] Other C-functionalized XÀCP compounds (X = R 3 Si, [6] R 2 N, [7,8] RO, [8] F, [9] Cl, [10] ), anionic species [XÀCP] À (X = R 3 B, [11] RN, [8] O, [12] S [13] ), and the cationic phosphonio phosphaalkyne [R 3 P À C P] + , [14] have been synthesized, but the vast majority of reports deal with tert-butyl, [15] adamantyl, [16] 2,4,6-trimethylphenyl [17] and 2,4,6-tri-tert-butylphenyl [18] phosphaalkynes. Recently, we devised a very simple method for accessing the kinetically stable crystalline triphenylmethyl (trityl)-substituted phosphaalkyne, Ph 3 CC P (1), which allowed for the economical metal-promoted synthesis of phosphorus heterocycles. However, our ultimate goal and incentive for synthesizing the trityl-substituted phosphaalkyne was to find an adequate leaving group that would lead us to cyaphide. [19] Treatment of 1 or its complexes [MH(dppe) 2 (Ph 3 C-CP)]OTf (M = Fe or Ru; dppe = bis(1,2-diphenylphosphinoethane); OTf = trifluoromethanesulfonate) with nucleophiles (Nu) did not furnish the desired cyaphide, C P À , or its complexes [Eq. (1); electrophile (E) = C].Therefore, we reasoned that silicon would be more susceptible to nucleophilic attack (E = Si) and applied an analogous synthetic procedure to access the higher homologue Ph 3 SiCP (3).Conversion of Ph 3 SiCH 2 Cl into the Grignard reagent followed by treatment with PCl 3 produced the silyl-substituted alkyl phosphonous dichloride, Ph 3 SiCH 2 PCl 2 (2), in over 87 % yield (Scheme 1). Employing 2.2 equiv of DABCO (1,8-diazabicyclo[2.2.2]octane) effected the dehydrohalogenation reaction, and 2 was fully transformed into the triphenylsilyl-substituted phosphaalkyne 3. The reaction occurred at ambient temperature and in multiple solvents in less than one hour. (In contrast, the reaction of DABCO with Ph 3 CCH 2 PCl 2 to furnish Ph 3 CC P required a 10-fold excess of base, elevated temperatures, and proceeded best in acetonitrile.[19] ) While DABCO alone was effective for the conversion of 2 into 3, we saw rapid decomposition of this new phosphaalkyne, which was dependent on the solvent. Qualitatively, the rate of decomposition of 3 followed the order Et 2 O % toluene < THF ! CH 3 CN. Suspecting that DABCO-HCl was acting as a soluble source of chloride anion in the more polar solvents that then attacked silicon to produce Ph 3 SiCl and the CP anion, which is seemingly unstable under the reaction conditions, we added AgOTf to the reaction mixture. When a solution of 2 in toluene was pretreated with 2.2 equiv of AgOTf for 5 min followed by addition of 2.2 equi...

Making the True “CP” Ligand

“…However, our ultimate goal and incentive for synthesizing the trityl-substituted phosphaalkyne was to find an adequate leaving group that would lead us to cyaphide. [19] Treatment of 1 or its complexes [MH(dppe) 2 (Ph 3 C-CP)]OTf (M = Fe or Ru; dppe = bis(1,2-diphenylphosphinoethane); OTf = trifluoromethanesulfonate) with nucleophiles (Nu) did not furnish the desired cyaphide, C P À , or its complexes [Eq. (1); electrophile (E) = C].…”

Azidanaloge Organophosphorchemie: RNP2 als Ligand und P2‐Quelle

“…À [9] sowie der Komplex [(Ph 2 PCH 2 CH 2 PPh 2 ) 2 Ru(H)(C P)] [10] mit einem terminalen PhosphaethinylLiganden zu werten. [11] N 2 ist das bislang einzige Allotrop des Elements Stickstoff.…”

Cyaphid, CP−: das Phosphor‐Analogon des Cyanids, CN−

“…[1] Der einzige zuvor bekannte Über-gangsmetallkomplex, von dem angenommen wurde, dass er einen terminalen CP 4 ] synthetisiert wurde (Schema 1). [6] Die Reaktion beginnt vermutlich mit der Insertion des Pd-Zentrums in die C-Cl-Bindung von 3, woran sich der Transfer der 2,4,6-Tritert-butylphenyl-Gruppe vom Phosphoratom zum Pd-Zentrum und die Spaltung der Pt-und Pd-Komplexe anschließt.…”

“…(6) ) ist länger als die Dreifachbindungen in Phosphaalkinen RC P (1.536(2) für R = tert-Butyl, [1] 1.52(1) für R = 2,4,6-Tri-tert-butylphenyl) und die C P-Bindung in [(dppe) 2 Ru(H)(CP)] (2; 1.573(2) ). [4] Der bindungsverlängernde Effekt der h 2 -Koordination auf die CP-Bindung wird auch in [(Ph 3 P) 2 Pt(h 2 -tBuCP)] beobachtet, in dem die C P-Bindung (1.67(2) ) länger ist als in nichtkoordiniertem tBuC P (1.536(2) ). Somit entspricht die CP-Bindung in 6 fast einer Doppelbindung in beispielsweise (Mesityl)P=CPh 2 (1.692(3) ) oder Ph(H)C = PR (1.67 für R = 2,4,6-Tritert-butylphenyl).…”

“…[1,6] Die Gegenwart der trans-{Pt(PEt 3 ) 2 (Cl)(CP) [6] Das einzige weitere Lewis-Säure-Addukt des CP À -Ions neben den erwähnten Übergangsmetallkomplexen ist die Verbindung (CF 3 ) 3 BCP À (9). [5] Wie in Gleichung (3) dargestellt ist, 4 -Salz 9 wurde in 91 % Ausbeute isoliert. Eine Röntgen-strukturanalyse der Verbindung zeigte eine annähernd tetraedrische Anordnung der vier Gruppen um das Boratom und eine C P-Bindungslänge von 1.563(10) , ähnlich der in tBuC P (1.536 (2) ).…”