Isolation of a Carbene‐Stabilized Phosphorus Mononitride and Its Radical Cation (PN^+.)

Abstract

In contrast to the inert nature of N 2 , diphosphorus (P 2 )[1] and diarsenic (As 2 ) [2] are only persistent in the gas phase at high temperatures; otherwise, they dimerize to form the stable tetrahedral white phosphorus (P 4 ) and yellow arsenic (As 4 ). Phosphorus mononitride (PN) has attracted a lot of interest, [3] mostly because it is an important component of the interstellar medium and the atmospheres of Jupiter and Saturn. [4] In the laboratory, gaseous PN has been synthesized by pyrolysis of different precursors, and the phosphorus-nitrogen bond length (1.49 ) determined by microwave spectroscopy.[5] In the condensed phase, PN is even more prone to association than P 2 and As 2 . Its dimer, P 2 N 2 , has not yet been detected experimentally, and its trimer has only been observed spectroscopically in a krypton matrix at 40 K. [6] Although the combination of two Group 15 elements does not preclude the isolation of small clusters, as shown by the recent discovery of AsP 3 , [7] the smallest discrete binary PN molecule that has been structurally characterized is P 3 N 21 . [8,9] [11g] only a single report describes the reaction of PN with metal atoms of Group 11 at 10 K.[12] The corresponding complexes have only been characterized by IR spectroscopy, and the description as monomeric PN complexes has been debated. [3d] Recently, it was shown that, just like transition metals, stable singlet carbenes can activate small molecules.[13] They also coordinate main group elements in their zero oxidation state, [14] leading to stable species such as carbodicarbenes (bent allenes) A [15,16] and diatomic silicon B 1 , [17a] germanium B 2 , [17b] phosphorous C 1 , [13e, 18] and arsenic C 2 [19] (Scheme 1). Herein we report the isolation of phosphorus mononitride stabilized by two carbenes. We also describe the one-electron oxidation of PN, which allows the complete characterization of the first isolable PN radical cation.The nitrogen atom was installed by treatment of NHC 1 [20] with bromine, followed by addition of aqueous ammonia. Deprotonation of 2 with nBuLi and addition of phosphorus trichloride afforded compound 3 in 68 % yield. The desired product 5 was then obtained in 88 % yield by reacting 3 with cyclic alkyl amino carbene (CAAC) 4[21] and subsequent reduction with excess magnesium (Scheme 2).Compound 5 is indefinitely stable, even in air at room temperature, both in the solid state and in solution. The 31 P NMR signal (d = + 134.0 ppm) appears at lower field than those of C 1 (d = + 59.4-À73.6 ppm), [18] which is expected because of the difference of electronegativity between nitrogen and phosphorus. Single crystals of 5 melt at 215 8C, and no decomposition was observed by heating a toluene solution under reflux for 24 h. According to the X-ray diffraction study [22] (Figure 1 a), compound 5 has a planar trans-bent geometry (N1-P1-C4 102.788, C1-N1-P1 122.128, C1-N1-P1-C4 torsion angle 179.388). Both the P1ÀC4 (1.719 ) and C1À N1 (1.282 ) bonds are rather short, and the central P À N bond (1.7085 )...

Synthesis and EPR/UV/Vis‐NIR Spectroelectrochemical Investigation of a Persistent Phosphanyl Radical Dication

“…After workup,t he extremely air-a nd moisture sensitive P-centered radical dication 13 2+ C was isolated as red powder in good yield as triflate salt (73 %, Scheme 4). This hyperfine coupling constant is comparable to those observed for other phosphanyl radicals [3][4][5][6][7][8][9] with at ypical range of a( 31 P) = 42-99 G. Interestingly,n oh yperfine coupling is observed to the 14 Natoms,i ndicating that the singly occupied molecular orbital (SOMO) is barely delocalized over the p-conjugated substituents but located primarily at the Patom. This hyperfine coupling constant is comparable to those observed for other phosphanyl radicals [3][4][5][6][7][8][9] with at ypical range of a( 31 P) = 42-99 G. Interestingly,n oh yperfine coupling is observed to the 14 Natoms,i ndicating that the singly occupied molecular orbital (SOMO) is barely delocalized over the p-conjugated substituents but located primarily at the Patom.…”

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The reaction of the bis(imidazoliumyl)-substituted P I cation [(2-Im Dipp )P(4-Im Dipp )] + (10 + )(2-Im = imidazolium-2-yl;4 -Im = imidazolium-4-yl;D ipp = 2,6-di-isopropylphenyl) with trifluoromethanesulfonic acid (HOTf) or methyl trifluoromethylsulfonate (MeOTf) yields the corresponding protonated [(2-Im Dipp )PH(4-Im Dipp )] 2+ (11 2+ )a nd methylated [(2-Im Dipp )PMe(4-Im Dipp )] 2+ (12 2+ )d ications, respectively.E PR/UV/Vis-NIR spectroelectrochemical investigation of the low-coordinated P I cation 10 + predicted astable and "bottleable" P-centered radical dication [(2-Im Dipp )P(4-Im Dipp )] 2+ C (13 2+ C). [2] However, only af ew examples are known that are stable enough to be isolated in the solid state.Representative examples of isolated and structurally characterized neutral (1C-5C), [3][4][5][6] anionic (6 À C), [7] and cationic (7 + C, 8 + C) [8,9] derivatives are depicted in Scheme 1. Quantum chemical investigation revealed an exceptional high spin density at the Patom.

Among several bonding motifs possible for charged and uncharged P 1 -centered radicals,p hosphanyl radicals are particularly intriguing.

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Isolation and Structure of Germylene‐Germyliumylidenes Stabilized by N‐Heterocyclic Imines

“…Since the seminal report on monomeric bis(amido) germylene and stannylene comprising aE N 2 Si (E = Ge,S n, Pb) scaffold by Veith and co-workers (D,F igure 1), [11] ar apidly growing number of papers have been published concerning the research on N-heterocyclic metallylenes. [17] These studies reveal that the imidazolin-2-imino group is particularly efficient in the stabilization of electrondeficient species.Herein we describe the isolation of hitherto unknown cationic germanium heterocycles and anew spacerseparated bis(germylene) bistriflate with pronounced bis(germyliumylidene) character. [12] We reported the isolation of the imidazolin-2-iminosubstituted Ge II and Sn II monocations E containing af ourmembered EN 2 Si (E = Ge,S n) ring system ( Figure 1).…”

Anorganische Chemie 2010

“…Dieses Kation kann auch als carbenstabilisiertes Phospheniumylradikal betrachtet werden, das aufgrund des sterischen Anspruchs der Substituenten nicht dimerisiert 1_55. Das eigentlich gasförmige Phosphormononitrid PN, eine binäre Interpniktogenverbindung, lässt sich ebenfalls als Bis(Carben)‐Addukt (49) isolieren und einfach zum entsprechenden Radikalkation oxidieren 1_56…”