Canadian Journal of Chemistry
An Unexpected Staudinger Reaction at an N-Heterocyclic Carbene-carbon Center
Journal: Canadian Journal of Chemistry
Manuscript ID cjc-2017-0607.R1
Manuscript Type: Article
Date Submitted by the Author: 08-Jan-2018
Complete List of Authors: Roy, Matthew; University of Alberta Department of Chemistry Miao, Linkun; University of Alberta Department of Chemistry Ferguson, Michael; University of Alberta Department of Chemistry McDonald, DraftRobert; University of Alberta, Chemistry Rivard, Eric; University of Alberta, Chemistry
Is the invited manuscript for consideration in a Special N Burford Issue?:
Keyword: Staudinger reaction, phosphazenes, carbene, phosphine
https://mc06.manuscriptcentral.com/cjc-pubs Page 1 of 17 Canadian Journal of Chemistry
An Unexpected Staudinger Reaction at an N-Heterocyclic Carbene-carbon Center§
Matthew M. D. Roy, Linkun Miao, Michael J. Ferguson, Robert McDonald, Eric Rivard* Department of Chemistry, University of Alberta, 11227 Saskatchewan Dr., Edmonton, AB, Canada, T6G 2G2
§ This paper is dedicated to Prof. Neil Burford in recognition of his profoundly important scientific and mentorship contributions to the chemical community in Canada.
Abstract
The previously unreported carbene phosphine adduct (IPr)PCl2N3, [IPr = (HCNDipp)2C:; Dipp = i Draft 2,6 Pr2C6H3] was synthesized and used as a synthon toward the elusive dichlorophosphazene
monomer unit, [Cl2P=N]. (IPr)PCl2N3 was found to undergo halide and azide abstraction when combined with various electrophiles and its thermolysis yielded the unexpected Staudinger
reaction product (IPr=N)PCl2.
Introduction
Originally referred to as ‘inorganic rubber’, poly(dichlorophosphazene) [Cl2P=N]n was first reported by Stokes in 1895.1 This important parent polymer is typically synthesized by the ring
opening polymerization (ROP) of hexachlorophosphazene [Cl2P=N]3, however it was initially of little practical importance due to its propensity to undergo hydrolysis. Later, Allcock and
coworkers pioneered the synthesis of well defined air stable polyphosphazenes [R2P=N]n via the substitution of main chain chlorine atoms in poly(dichlorophosphazene) with various alkoxides, aryloxides and amides.2 During the search for alternate paths to polyphosphazenes and to gain insight into the ROP mechanism,3 the reactivity of hexachlorophosphazene with Lewis acids4 and Lewis bases5 has been explored. Notably, when reacted with Lewis acids and bases the
cyclic nature of [Cl2P=N]3 is generally maintained with the phosphorus centers behaving as electron acceptors and nitrogen atoms as donors. As such, we looked to prepare a
dichlorophosphazene monomer [Cl2P=N] through a bottom up approach that may allow for the
1 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 2 of 17
controlled delivery of the [Cl2P=N] unit for materials synthesis; this work gains added inspiration from the selective construction of P N chains via condensation chemistry6 and the 7 impressive recent isolation of monomeric phosphazenes R2PN via kinetic stabilization. Our group has utilized a donor acceptor concept to isolate various reactive main group species, typically relying on N heterocyclic carbenes (NHCs) or N heterocyclic olefins (NHOs) as ligands.8,9 Perhaps most relevant to the work described in this paper, we have observed that the inorganic acetylene complexes (NHC)HB=NH(LA), (LA = Lewis acid) can be synthesized by thermolysis of carbene supported azidoboranes (NHC)BH2N3 in the presence of an appropriately bulky Lewis acid.10 We therefore looked to apply a similar dinitrogen extrusion 11 protocol to yield (NHC)Cl2P=N(LA), a masked source of [Cl2P=N]. While we were not successful in preparing the desired species, an interesting NHC supported phosphine azide 12 i adduct was synthesized, (IPr)PCl2N3 [IPr = (HCNDipp)2C:; Dipp = 2,6 Pr2C6H3], and its
subsequent thermal rearrangement to the monomeric iminophosphine (IPr=N)PCl2 was observed. (IPr=N)PCl2 is a potential precursor to Drafta wide range of strongly electron donating ligands of the 13 general form (IPr=N)PR2. The latter transformation, to our knowledge, represents an example of a Staudinger reaction at a carbene carbon center in preference over a proximal phosphine, and the energetics of this rearrangement were studied computationally. The Lewis basicity of the resulting iminophosphine was demonstrated by the synthesis of the stable phosphine borane
adduct (IPr=N)PCl2•BH3. Results and discussion F With the goal of forming the [Cl2P=N] donor acceptor species (IPr)Cl2P=N(BAr 3), the n F F soluble azide source [ Bu4N]N3 was first combined with BAr 3 (Ar = 3,5 (CF3)2C6H3) in n F fluorobenzene, leading to the in situ formation of the azidoborate [ Bu4N]N3 BAr 3 after one 11 1 19 1 14 hour [broad B{ H} resonance at 0.6 ppm and a F{ H} resonance at 62.2 ppm in C6D6]. n F 15 [ Bu4N]N3 BAr 3 was then added to the known complex (IPr)PCl3 with the intension of F yielding (IPr)Cl2PN(BAr 3) in a one pot fashion (via initial Cl/N3 exchange to yield the F 10 1 intermediate (IPr)Cl2PN3(BAr 3) accompanied by the loss of N2 (Scheme 1). The H NMR spectrum of the product mixture after 90 minutes of stirring at room temperature revealed several n + species including the presence of unreacted (IPr)PCl3, a highly soluble [ Bu4N] salt, and a new IPr containing product. Crystallization of the reaction mixture afforded crystals of the new azidophosphine adduct (IPr)PCl2N3 (1) which was contaminated with ca. 50% of co crystallized
2 https://mc06.manuscriptcentral.com/cjc-pubs Page 3 of 17 Canadian Journal of Chemistry
(IPr)PCl3 (Fig. S4); in the case of 1, substitution of an equatorially bound chloride by azide transpired, with an overall T shaped geometry at phosphorus.
F Scheme 1. Possible synthetic route to the target species (IPr)Cl2P=N(BAr 3).
Draft
Scheme 2. Synthesis of (IPr)PCl2N3 (1) and its thermal rearrangement to (IPr=N)PCl2 (2).
While this direct approach did not afford the target species (as it did for our reported HB=NH 10 adducts), we looked to prepare (IPr)PCl2N3 (1) in an alternate fashion. As such, when Me3Si
N3 was added to a toluene slurry of (IPr)PCl3 and the mixture stirred for one hour, (IPr)PCl2N3 (1) was obtained as a colorless solid in 94 % yield (Scheme 2) with 1H and 31P{1H} NMR
spectra which matched that of the major product formed in the above reaction between (IPr)PCl3 n F and [ Bu4N]N3 BAr 3 (Scheme 2). From this reaction mixture, pure crystals of (IPr)PCl2N3 were obtained and the structure of 1 was determined by single crystal X ray crystallography (Fig. 1).
3 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 4 of 17
Fig. 1. Molecular structure of (IPr)PCl2N3 (1) with thermal ellipsoids plotted at the 30% probability level. All hydrogen atoms and fluorobenzene solvent have been omitted for clarity. Selected bond lengths [Å] and angles [°]: C1 P 1.8762(15), P Cl1 2.1950(6), P Cl2 2.5263(6), P N3 1.7426(16), N3 N4 1.225(2), N4 N5Draft 1.126(3); Cl1 P Cl2 179.52(2), Cl1 P N3 89.57(6), Cl1 P C1 93.20(5), C1 P N3 98.34(7).
The molecular structure of 1 shows an expected distorted T shaped geometry, 16 corresponding to an overall AEX4 VSEPR arrangement, indicating the presence of a stereochemically active phosphorus lone pair. One P Cl bond in 1 is significantly elongated relative to the other [P Cl(1) = 2.1950(6) Å versus P Cl(2) = 2.5263(6) Å] and could be a consequence of the strong donor ability of the N heterocyclic carbene IPr, which in turn lowers the Lewis acidity of the phosphorus atom in 1. Additionally, the CNHC P distance [1.8762(15) Å] 15 compares well with that of (IPr)PCl3 [1.871(11) Å]. Curious as to whether thermolysis of 1 would yield an NHC supported phosphinonitrene (R2PN) or dichlorophosphazene oligomers via
N2 loss, compound 1 was heated to 80 °C in toluene for one hour (Caution!). As expected, the visible release of a gas from solution was noted and 31P{1H} NMR analysis of the resulting colorless solution revealed the complete disappearance of 1 (δ 6.7 ppm) along with the formation of a new product with a down field shifted 31P{1H} NMR resonance of 166.4 ppm; the latter 17 resonance is in the range normally seen for monosubstituted phosphorus(III) dihalides RPCl2, suggesting that the expected Staudinger type oxidation at phosphorus to yield a P(V) species did
4 https://mc06.manuscriptcentral.com/cjc-pubs Page 5 of 17 Canadian Journal of Chemistry
not occur.18 However, X ray analysis of crystals of this product did show that a Staudinger reaction transpired, however via oxidation of the N heterocyclic carbene ligand (and concomitant 19 loss of N2) to yield the new N heterocyclic imine substituted phosphine (IPr=N)PCl2 (2) in an 88 % yield (Scheme 3). Bertrand and coworkers have prepared the backbone saturated
phosphine imine (SIPr=N)PCl2, [SIPr = (H2CNDipp)2C] by combining the lithiated imide 20 [SIPr=N]Li with PCl3. As an alternative, we have also found that (IPr=N)PCl2 (2) can be
synthesized directly from IPr=N SiMe3 and PCl3, with a slightly higher overall yield of 93 % versus the thermal rearrangement route mentioned above.
Draft
Fig. 2. Molecular structure of (IPr=N)PCl2 (2) with thermal ellipsoids plotted at the 30% probability level. All hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles [°]: C1 N3 1.319(3), N3 P 1.6023(17), P Cl1 2.1383(9), P Cl2 2.1077(8); C1 N3 P 127.64(15), Cl1 P Cl2 95.01(3), Cl1 P N3 100.30(7), Cl2 P N3 101.90(7).
The structure of (IPr=N)PCl2 (2) (Fig. 2) showed metrical parameters consistent with the structure depicted in Scheme 2, with a P N single bond length [1.6023(17) Å] that is shorter than
the P N bond distance of 1.7426(16) found in the azido phosphine adduct (IPr)PCl2N3 (1). Moreover the internal IPr=N imine C=N double bond adopts a distance of 1.319(3) Å, in line
with the retention of substantial double bond character, while the CIPr=N P bond angle is 127.64(15)°, consistent with the presence of formal sp2 hybridization at nitrogen.
5 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 6 of 17
The lone pair at the phosphorus(III) center in (IPr=N)PCl2 (2) was found to be chemically active, as evidenced by the reaction between 2 and Me2S•BH3 (Equation 1). The resulting stable dihalophosphine borane adduct (IPr=N)PCl2•BH3 (3) was generated in a nearly quantitative yield 1 11 2 (95 %) and the associated H{ B} NMR spectrum in C6D6 showed a doublet resonance ( JHP = 31 1 11 1 11.0 Hz, P BH3), along with broad doublet signals in the P{ H} and B{ H} NMR spectra 1 arising from discernable JPB coupling (ca. 67 Hz). The structure of 3 was further confirmed by
X ray crystallography (Fig. 3). Upon BH3 coordination, the IPr=N bond length remains nearly identical to 2 [1.324(2) Å] and a significant widening of the C1 N3 P angle is present [143.70(14)° in 3 versus 127.64(15)° in 2].
Draft
Fig. 3. Molecular structure of (IPr=N)PCl2•BH3 (3) with thermal ellipsoids plotted at the 30% probability level. All carbon bound hydrogen atoms and fluorobenzene solvent have been omitted for clarity. Selected bond lengths [Å] and angles [°]: C1 N3 1.324(2), N3 P 1.5502(15), P Cl1 2.0604(7), P Cl2 2.0652(8), P B 1.890(3), C1 N3 P 143.70(14), Cl1 P N3 112.32(6), Cl2 P N3 108.65(7), N3 P B 117.51(13).
6 https://mc06.manuscriptcentral.com/cjc-pubs Page 7 of 17 Canadian Journal of Chemistry
In order to probe the energetics associated with the thermal rearrangement of (IPr)PCl2N3
(1) into (IPr=N)PCl2 (2), the dissociation of 1 was computed (Equation 2). As expected, rupture
of the dative CNHC P linkage was found to be both endothermic ( rH = 17.6 kcal/mol) and
endergonic ( rG = 2.1 kcal/mol). The subsequent formation of 2 from free IPr and PCl2N3
(Equation 3) was computed to be significantly exothermic ( rH = 88.8 kcal/mol) and exergonic,
( rG = 86.1 kcal/mol), and driven by the formation of N2. This resulted in an overall exothermic ( H = 71.2 kcal/mol) and exergonic ( G = 84.0 kcal/mol) process (Equation 4) for the transformation of 1 into 2. Draft
We were then interested to further explore the reactivity of (IPr)PCl2N3 (1), namely to see whether Lewis acids would coordinate to the phosphorus pendent azide group and induce the
7 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 8 of 17
formation of donor acceptor complexes of [Cl2P=N]. Initially, BEt3 was combined with 1 in toluene (Scheme 3), however rather than azide coordination, we observed exclusively the 21 formation of (IPr)BEt3, presumably with the loss of the potentially volatile PCl2N3 (Caution!); 22 given the possible risks associated with the liberation of PCl2N3, we did not investigate this line of reactivity further with BEt3.
Draft Scheme 3. The reactivity of (IPr)PCl2N3 (1) toward various Lewis acids (LA) and Me3Si OTf.
F When compound 1 was combined with the strong Lewis acids AlCl3, B(C6F5)3 or BAr 3, intractable mixtures containing several unidentified species were formed, tentatively assigned as + + 31 1 mixtures of [(IPr)PCl2] and [(IPr)PCl(N3)] . For example, a P{ H} NMR spectrum from the reaction of 1 with B(C6F5)3 showed the complete consumption of 1 and the formation of several products, including two major products with signals at δ 112.9 ppm (ca. 27 %) and δ 100.7 ppm 12a (ca. 68 %), that closely match those found for the known compounds [(IPr)PCl2]OTf (δ 113.7 12b ppm) and [(IPr)PCl(N3)]OTf (δ 104.0 ppm), respectively. Similar observations were noted for F the reaction of 1 with either AlCl3 or BAr 3. All attempts to obtain pure products via fractional + crystallization yielded poorly diffracting crystals consisting of co crystallized [(IPr)PCl(N3)] + F and [(IPr)PCl2] cations with Cl/N3 LA anions (LA = AlCl3, B(C6F5)5 and BAr 3) resulting from + concurrent chloride and azide abstraction from 1. Looking to form [(IPr)PCl(N3)] in a controlled 31 1 fashion, 1 was combined with one equiv. of the electrophile Me3Si OTf. The P{ H} NMR 12a spectrum in CD3CN revealed the formation of [(IPr)PCl2]OTf (δ 113.7 ppm, ca. 17%), along 12b with the previously reported compound [(IPr)P(N3)2]OTf (δ 104.0 ppm, ca. 16%), and the
8 https://mc06.manuscriptcentral.com/cjc-pubs Page 9 of 17 Canadian Journal of Chemistry
tentatively assigned species [(IPr)PCl(N3)]OTf (δ 103.5 ppm, 67%), again indicating that both chloride and azide abstraction were occurring.
Conclusions While we were not able to prepare the target dichlorophosphazene complex
(NHC)Cl2P=N(LA), a new NHC bound azidophosphine (IPr)PCl2N3 (1) was prepared as a room
temperature stable solid. The reactivity of 1 toward a variety of Lewis acids and Me3Si OTf was explored, giving evidence of non selective chloride and azide ion abstraction. Heating compound
1 afforded (IPr=N)PCl2 (2) in high yield via a Staudinger type reaction which favors azide
coupling (nitrene addition) to a carbene carbon center over a phosphorus(III) site. (IPr=N)PCl2 is a promising ligand precursor to N heterocyclic imine supported phosphines, which have been shown to be strong donors in the past.13b Future work will involve the use of non azide routes to accomplish nitrogen atom delivery23 in the main group. Draft Experimental data
General procedures
All reactions were performed in an inert atmosphere glovebox (Innovative Technology, Inc.). Solvents were dried using a Grubbs type solvent purification system24 manufactured by Innovative Technologies, Inc., degassed (freeze pump thaw method), and stored under an
atmosphere of nitrogen prior to use. PCl3 was purchased from Sigma Aldrich and distilled under
nitrogen prior to use. Me3Si N3 was purchased from Alfa Aesar and used as received. AlCl3 was purchased from Sigma Aldrich and sublimed under dynamic vacuum (ca. 10 3 torr) prior to use.
Me2S•BH3 was purchased as a 2.0 M solution in THF from Sigma Aldrich and used as received. 15 25 26 F F 27 (IPr)PCl3 and (IPr=N)SiMe3, B(C6F5)3, and BAr 3 (Ar = 3,5 (F3C)2C6H3)) were prepared according to literature procedures. 1H, 13C{1H} and 31P{1H} NMR spectra were recorded on 400, 1 500, 600 or 700 MHz Varian Inova instruments and were referenced externally to SiMe4 ( H, 13 1 31 1 11 1 C{ H}), 85 % H2PO4 ( P{ H}) or F3B•OEt2 ( B{ H}). Elemental analyses were performed by the Analytical and Instrumentation Laboratory at the University of Alberta. Melting points were measured in sealed glass capillaries under nitrogen by using a MelTemp apparatus.
9 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 10 of 17
X-ray crystallography
Crystals for X ray diffraction studies were removed from a vial (in a glovebox) and immediately coated with a thin layer of hydrocarbon oil (Paratone N). A suitable crystal was then mounted on a glass fiber and quickly placed in a low temperature stream of nitrogen on the X ray diffractometer.28 All data were collected using a Bruker APEX II CCD detector/D8 or PLATFORM diffractometer using Mo Kα or Cu Kα radiation, with the crystals cooled to – 80 °C or – 100 °C. The data were corrected for absorption through Gaussian integration from the indexing of the crystal faces. Crystal structures were solved using intrinsic phasing (SHELXT)29 and refined using SHELXL 2014.29 The assignment of hydrogen atom positions were based on the sp2 or sp3 hybridization geometries of their attached carbon atoms and were given thermal parameters 20 % greater than those of their parent atoms Draft
(IPr)PCl2N3 (1)
To a vial containing a slurry of (IPr)PCl3 (0.291g, 0.552 mmol) in 15 mL of toluene was
added Me3SiN3 (73.4 µL, 0.553 mmol). The reaction mixture was stirred for 1 hr and the volatiles were removed from the colorless slurry in vacuo to afford 1 as a colorless solid (0.278 g, 94 %). Colorless crystals suitable for X ray crystallographic analysis were obtained by
layering a fluorobenzene solution of (IPr)PCl2N3 (1) with hexanes and storing in a 30 °C freezer 1 3 for 2 days. H NMR (THF d8, 498.1 MHz): δ 7.82 (s, 2H, NCH), 7.53 (t, 2H, JHH = 8.0 Hz, p 3 3 ArH), 7.39 (d, 4H, JHH = 8.0 Hz, m ArH), 3.17 (broad septet, 4H, JHH = 6.5 Hz, CH(CH3)2), 3 3 13 1 1.42 (d, 12H, JHH = 6.5 Hz, CH(CH3)2), 1.11 (d, 12H, JHH = 6.5 Hz, CH(CH3)2). C{ H} NMR
(THF d8, 125.3 MHz): δ 147.4 (NCH), 132.1 (ArC), 126.9 (ArC), 125.0 (ArC), 124.8 (ArC),
29.9 (CH(CH3)2), 26.2 (CH(CH3)2), 23.1 (CH(CH3)2). An NCN resonance was not found. 31 1 1 P{ H} NMR (THF d8, 201.6 MHz): δ 11.3. M.p. 153 °C (decomp.). IR (Nujol, cm ): 2132 (m,
ν N3). Elemental analyses were performed on three different samples. In all cases the CHN values were systematically high in carbon content. Relevant NMR spectra are given in Fig. S1 S3.30
10 https://mc06.manuscriptcentral.com/cjc-pubs Page 11 of 17 Canadian Journal of Chemistry
(IPr=N)PCl2 (2)
Route A:
A thick walled Schlenk flask was loaded with a slurry of (IPr)PCl2N3, (0.153 g, 0.287 mmol) in ca. 18 mL toluene, partially evacuated, and sealed with a J Young joint. The flask was then heated to 80 °C for 1 hr (Caution!) where bubbling was observed, forming a pale orange slurry. The slurry was then returned to the glovebox and transferred to a vial where the volatiles were removed in vacuo yielding 2 as an off white solid (0.128 g, 88 %). Colorless crystals suitable for X ray crystallographic analysis were obtained by storing a fluorobenzene solution of
(IPr=N)PCl2 (2) in a 30 °C freezer overnight.
Route B:
To a vial containing a 15 mL solution of (IPr=N)SiMe3 (0.396 g, 0.831 mmol) in toluene was
added PCl3 (72.8 µL, 0.832 mmol). The resulting slurry was stirred for 1 hr and the volatiles were removed in vacuo yielding 2 as anDraft off white solid (0.390 g, 93 %).
1 3 Analytical Data for 2: H NMR (C6D6, 399.8 MHz): δ 7.17 (t, 2H, JHH = 8.0 Hz, p ArH), 7.06 3 3 (d, 4H, JHH = 8.0 Hz, m ArH), 5.94 (s, 2H, NCH), 2.88 (septet, 4H, JHH = 6.8 Hz, CH(CH3)2), 3 3 1.40 (broad d, 12 H, JHH = 6.8 Hz, CH(CH3)2), 1.07 (broad d, 12 H, JHH = 6.8 Hz, CH(CH3)2). 13 1 C{ H} NMR (C6D6, 125.7 MHz): δ 147.0 (ArC), 132.2 (ArC), 131.0 (ArC), 124.6 (ArC), 116.8
(NCH), 29.3 (CH(CH3)2), 24.7 (CH(CH3)2), 23.4 (CH(CH3)2). An NCN resonance was not 31 1 observed. P{ H} NMR (C6D6, 161.8 MHz): δ 166.4. M.p. 221 °C (decomp.). Anal. Calcd. for
C27H36Cl2N3P: C 64.28, H 7.19, N 8.33. Found: C 63.76, H 7.21, N 7.53.
(IPr=N)PCl2•BH3 (3)
To a vial containing a 15 mL THF slurry of (IPr=N)PCl2 (0.231 g, 0.457 mmol) was
added a 2.0 M THF solution of (H3C)2S•BH3 (228.8 L, 0.458 mmol). The reaction mixture was stirred for 1 hr and the resultant slurry was concentrated to dryness in vacuo affording 3 as an off white solid (0.225 g, 95 %). Colorless crystals suitable for X ray crystallographic analysis
were obtained by storing a fluorobenzene solution of (IPr=N)PCl2•BH3 (3) in a 30 °C freezer for 1 11 3 3 days. H{ B} NMR (C6D6, 498.1 MHz): δ 7.17 (t, 2H, JHH = 8.0 Hz, p ArH), 7.05 (d, 4H,
11 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 12 of 17
3 3 JHH = 8.0 Hz, m ArH), 6.04 (s, 2H, NCH), 2.79 (septet, 4H, JHH = 6.5 Hz, CH(CH3)2), 2.02 (d, 2 3 3 3H, JHP = 11.0 Hz, P BH3), 1.41 (d, 12 H, JHH = 6.5 Hz, CH(CH3)2), 1.03 (d, 12 H, JHH = 7.0 13 1 Hz, CH(CH3)2). C{ H} NMR (C6D6, 125.7 MHz): δ 146.6 (ArC), 131.5 (ArC), 131.2 (ArC), 31 1 124.7 (ArC), 117.8 (NCH), 29.3 (CH(CH3)2), 25.2 (CH(CH3)2), 23.2 (CH(CH3)2). P{ H} NMR 1 11 1 (C6D6, 201.6 MHz): δ 85.6 (broad d, JPB = 66.5 Hz). B{ H} NMR (C6D6, 159.8 MHz): δ 24.9 1 (broad d, JPB = 49.1 Hz). M.p. 165 °C (decomp.). Anal. Calcd. for C27H39BCl2N3P: C 62.57, H 7.58, N 8.11. Found: C 63.42, H 7.83, N 7.55.
Reaction of 1 with Me3Si-OTf
To a vial containing a ca. 10 mL toluene slurry of (IPr)PCl2N3 (0.134 g, 0.252 mmol) was added
Me3Si OTf (45.4 L, 0.251 mmol) and the resulting colorless slurry was stirred for 1 hour. A ca. 1 mL aliquot was removed from the reaction mixture and the volatiles were removed in vacuo yielding a colorless solid. A 31P{1H} NMRDraft assay of the solid revealed the complete consumption 12a of (IPr)PCl2N3 and the formation of the known products [(IPr)PCl2]OTf and 12b 31 1 [(IPr)P(N3)2]OTf, and a new signal tentatively assigned to [(IPr)PCl(N3)]OTf. P{ H} NMR
(CD3CN, 161.8 MHz): δ 113.7 (17%, [(IPr)PCl2]OTf), 104.0 (16 %, [(IPr)P(N3)2]OTf), 103.5
(67 %, [(IPr)PCl(N3)]OTf). Attempts to isolate the major product by crystallization from toluene, THF, or fluorobenzene were unsuccessful.
Acknowledgements: We thank NSERC of Canada for financial support of this work (DG and CREATE grants for E.R.; CREATE fellowship for M.M.D.R.; USRA for L.M.). E.R. thanks the Faculty of Science at the University of Alberta for a Research Fellowship and the Alexander von Humboldt Foundation for an Experienced Researcher Fellowship. We would also like to thank Dr. Anindya K. Swarnakar, Dr. Christian Hering Junghans and Dr. Michael P. Boone for helpful discussions.
References
1. (a) Stokes, H. N. Am. Chem. J. 1895, 17, 275; (b) Stokes, H. N. Am. Chem. J. 1896, 18, 629.
12 https://mc06.manuscriptcentral.com/cjc-pubs Page 13 of 17 Canadian Journal of Chemistry
2. (a) Allcock, H. R.; Kugel, R. L. J. Am. Chem. Soc. 1965, 87, 4216. doi: 10.1021/ja01096a056; (b) Allcock, H. R.; Kugel, R. L.; Valen, K. J. Inorg. Chem. 1966, 5, 1709. doi: 10.1021/ic50044a016; (c) Allcock, H. R.; Kugel, R. L. Inorg. Chem. 1966, 5, 1716. doi: 10.1021/ic50044a017; For selected review articles, see: (d) Neilson, R. H.; Wisian Neilson, P. Chem. Rev. 1988, 88, 541. doi: 10.1021/cr00085a005; (e) Allen, C. W. Coord. Chem. Rev. 1994, 130, 137. doi: 10.1016/0010 8545(94)80004 9; (f) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1602. doi: 10.1002/anie.199616021; (g) Priegert, A. M.; Rawe, B. W.; Serin, S. C.; Gates, D. P. Chem. Soc. Rev. 2016, 45, 922. doi: 10.1039/C5CS00725A 3. (a) Lund, L. G.; Paddock, N. L.; Proctor, J. E.; Searle, H. T. J. Chem. Soc. 1960, 2542. doi: 10.1039/JR9600002542; (b) Chandrasekhar, V.; Thilagar, P.; Pandian, B. M. Coord. Chem. Rev. 2007, 251, 1045. doi: 10.1016/j.ccr.2006.07.005; (c) Zhang, Y.; Huynh, K.; Manners, I.; Reed, C. A. Chem. Commun. 2008, 494. doi: 10.1039/B713933K. 4. Tun, Z. M.; Heston, A. J.; Panzner, M. J.; Medvetz, D. A.; Wright, B. D.; Savant, D.; Dudipala, V. R.; Banerjee, D.; Rinaldi,Draft P. L.; Youngs, W. J.; Tessier, C. A. Inorg. Chem. 2011, 50, 8937. doi: 10.1021/ic201075z, and references therein. 5. (a) Boomishankar, R.; Ledger, J.; Guilbaud, J. B.; Campbell, N. L.; Bacsa, J.; Bonar Law, R.; Khimyak, Y. Z.; Steiner, A. Chem. Commun. 2007, 5152. doi: 10.1039/B713847D; (b) Al Rafia, S. M. I.; Ferguson, M. J.; Rivard, E. Inorg. Chem. 2011, 50, 10543. doi: 10.1021/ic201812a. 6. (a) Honeyman, C. H.; Manners, I.; Morrissey, C. T.; Allcock, H. R. J. Am. Chem. Soc. 1995, 117, 7035. doi: 10.1021/ja00131a040; (b) Rivard, E.; Lough, A. J.; Manners, I. Inorg. Chem. 2004, 43, 2765. doi: 10.1021/ic049955z; (c) Rivard, E.; Huynh, K.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2004, 126, 2286. doi: 10.1021/ja039549z; (d) Huynh, K.; Lough, A. J.; Forgeron, M. A. M.; Bendle, M.; Presa Soto, A.; Wasylishen, R. E.; Manners, I. J. Am. Chem. Soc. 2011, 131, 7905. doi: 10.1021/ja900256g. 7. (a) Dielmann, F.; Back, O.; Henry Ellinger, M.; Jerabek, P.; Frenking, G.; Bertrand, G. Science 2012, 337, 1526. doi: 10.1126/science.1226022; (b) Dielmann, F.; Bertrand, G. Chem. Eur. J. 2015, 21, 191. doi: 10.1002/chem.201405430. 8. For relevant review articles, see: (a) Rivard, E. Dalton Trans. 2014, 43, 8577. doi: 10.1039/C4DT00481G; (b) Rivard, E. Chem. Soc. Rev. 2016, 45, 989. doi: 10.1039/C5CS00365B; (c) Roy, M. M. D.; Rivard, E. Acc. Chem. Res. 2017, 50, 2017. doi: 10.1021/acs.accounts.7b00264.
13 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 14 of 17
9. For the elegant use of Lewis bases to stabilize reactive phosphorus based species, see the following selected references: (a) Gray, P. A.; Burford, N. Coord. Chem. Rev. 2016, 324, 1. doi: 10.1016/j.ccr.2016.05.010; (b) Burford, N.; Cameron, T. S.; Ragogna, P. J.; Ocando Mavarez, E.; Gee, M.; McDonald, R.; Wasylichen, R. E. J. Am. Chem. Soc. 2001, 123, 7947. doi: 10.1021/ja011075l; (c) Schwedtmann, K.; Hennersdorf, F.; Bauzá, A.; Frontera, A.; Fischer, R.; Weigand, J. J. Angew. Chem., Int. Ed. 2017, 56, 6218. doi: 10.1002/anie.201702058; (d) Macdonald, C. L. B.; Binder, J. F.; Swidan, A.; Nguyen, J. H.; Kosnik, S. C.; Ellis, B. D. Inorg. Chem. 2016, 55, 7152. doi: 10.1021/acs.inorgchem.6b01163; (e) Dube, J. W.; Macdonald, C. L. B.; Ragogna, P. J. Angew. Chem., Int. Ed. 2012, 51, 13026. doi: 10.1002/anie.201205744; (f) Graham, C. E.; Pritchard, T. E.; Boyle, P. D.; Valjus, J.; Tuononen, H. M.; Ragogna, P. J. Angew. Chem., Int. Ed. 2017, 56, 6236. doi: 10.1002/anie.201611196; (g) Price, A. N.; Nichol, G. S.; Cowley, M. J. Angew. Chem., Int. Ed. 2017, 56, 9952. Doi: 10.1002/anie.201705050; (h) Wang, Y.; Hickox, H. P.; Xie, Y.; Wei, P.; Cui, D.; Walter, M. R.; Schaefer, H. F., III; Robinson, G. H. Chem. Commun. 2016, 52, 5746.Draft doi: 10.1039/C6CC01759B; (i) Majhi, P. K.; Chow, K. C. F.; Hsieh, T. H. H.; Bowes, E. G.; Schnakenburg, G.; Kennepohl, P.; Streubel, R.; Gates, D. P. Chem. Commun. 2016, 52, 998. doi: 10.1039/c5cc08181e; (j) Graham, C. M. E.; Millet, C. R. P.; Price, A. N.; Valjus, J.; Cowley, M. J.; Tuononen, H. M.; Ragogna, P. J. Chem. Eur. J. 2017, doi: 10.1002/chem.201704337. 10. (a) Swarnakar, A. K.; Hering Junghans, C.; Nagata, K.; Ferguson, M. J.; McDonald, R.; Tokitoh, N.; Rivard, E. Angew. Chem., Int. Ed. 2015, 54, 10666. doi: 10.1002/anie.201504867; (b) Swarnakar, A. K.; Hering Junghans, C.; Ferguson, M. J.; McDonald, R.; Rivard, E. Chem. Sci. 2017, 8, 2337, doi: 10.1039/C6SC04893E. 11. We have also shown that donor acceptor complexes can effectively release their trapped molecular cargo, as evidenced by the use of GeH2 complexes to yield luminescent germanium nanoparticles: (a) Purkait, T. P.; Swarnakar, A. K.; De Los Reyes, G. B.; Hegmann, F. A.; Rivard, E.; Veinot, J. G. C. Nanoscale 2015, 7, 2241. doi: 10.1039/C4NR05125D; (b) Thimer, K. C.; Al Rafia, S. M. I.; Ferguson, M. J.; McDonald, R.; Rivard, E. Chem. Commun. 2009, 7119. doi: 10.1039/B915950A. 12. For related examples of NHC stabilized P(III) azides and chlorides, see: (a) Henne, F. D.; Schnöckelborg, E. M.; Feldmann, K. O.; Grunenberg, J.; Wolf, R.; Weigand, J. J. Organometallics 2013, 32, 6674. doi: 10.1021/om4002268; (b) Henne, F. D.; Dickschat, A. T.;
14 https://mc06.manuscriptcentral.com/cjc-pubs Page 15 of 17 Canadian Journal of Chemistry
Hennersdorf, F.; Feldmann, K. O.; Weigand, J. J. Inorg. Chem. 2015, 54, 6849. doi: 10.1021/acs.inorgchem.5b00765. 13. (a) Dumrath, A.; Lübbe, C.; Neumann, H.; Jackstell, R.; Beller, M. Chem. Eur. J. 2011, 17, 9599. doi: 10.1002/chem.201100984; (b) Wünsche, M. A.; Mehlmann, P.; Witteler, T.; Buβ, F.; Rathmann, P.; Dielmann, F. Angew. Chem., Int. Ed. 2015, 54, 11857. doi:
10.1002/anie.201504993; for related (IPr=CH)PR2 ligands, see: (c) Paisley, N. R.; Lui, M. W.; McDonald, R.; Ferguson, M. J.; Rivard, E. Dalton Trans. 2016, 45, 9860. doi: 10.1039/C6DT00299D; (d) Lui, M. W.; Shynkaruk, O.; Oakley, M. S.; Sinelnikov, R.; McDonald, R.; Ferguson, M. J.; Meldrum, A.; Klobukowski, M.; Rivard, E. Dalton Trans. 2017, 46, 5946. doi: 10.1039/C7DT00398F. 14. For the related use of [N3 BR3] anions to yield Lewis acid coordinated uranium nitrides
(after N2 loss), see: Fox, A. R.; Arnold, P. L.; Cummins, C. C. J. Am. Chem. Soc. 2010, 132, 3250. doi: 10.1021/ja910364u. 15. Wang, Y.; Xie, Y.; Abraham, M. Y.;Draft Gilliard Jr., R. J.; Wei, P.; Schaefer III, H. F.; Schleyer, P. v. R.; Robinson, G. H. Organometallics 2010, 29, 4778. doi: 10.1021/om100335j. 16. Gillespie, R. J. Coord. Chem. Rev. 2008, 252, 1315.. doi: 10.1016/j.ccr.2007.07.007. 17. Burford, N.; Cameron, T. S.; Conroy, K. D.; Ellis, B.; Macdonald, C. L. B.; Ovans, R.; Phillips, A. D.; Ragogna, P. J.; Walsh, D. Can. J. Chem. 2002, 80, 1404. doi: 10.1139/V02 161. 18. Gololobov, Y. G.; Kasukhin, L. F. Tetrahedron 1992, 48, 1353. doi: 10.1016/S0040 4020(01)92229 X. 19. For reviews of N heterocyclic imines in main group chemistry, see: (a) Ochiai, T.; Franz, D.; Inoue, S. Chem. Soc. Rev. 2016, 45, 6327. doi: 10.1039/c6cs00163g; (b) Todd, A. D. K.; McClennan, W. L.; Masuda, J. D. RSC Adv. 2016, 6, 69270. Doi: 10.1039/C6RA15507C. 20. Kinjo, R.; Donnadieu, B.; Bertrand, G. Angew. Chem. Int. Ed. 2010, 49, 5930. doi: 10.1002/anie.201002889. 21. (a) Monot, J.; Brahmi, M. M.; Ueng, S. H.; Robert, C.; Murr, M. D. E.; Curran, D. P.; Malacria, M.; Fensterbank, L.; Lacôte, E. Org. Lett. 2009, 11, 4914. doi: 10.1021/ol902012c; (b) Al Rafia, S. M. I.; Lummis, P. A.; Swarnakar, A. K.; Deutsch, K. C.; Ferguson, M. J.; McDonald, R.; Rivard, E. Aust. J. Chem. 2013, 66, 1235. doi: 10.1071/CH13209. 22. Dillon, K. B.; Platt, A. W.; Waddington, T. C. J. Chem. Soc., Dalton Trans. 1980, 1036. doi: 10.1039/DT9800001036.
15 https://mc06.manuscriptcentral.com/cjc-pubs Canadian Journal of Chemistry Page 16 of 17
23. Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 6252. doi: 10.1021/ja048713v. 24. Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518. doi: 10.1021/om9503712. 25. Tamm, M.; Randoll, S.; Herdtweck, E.; Kleigrewe, N.; Kehr, G.; Erker, G.; Rieger, B. Dalton Trans. 2006, 459. doi: 10.1039/B511752F. 26. (a) Kuprat, M.; Lehmann, M.; Schulz, A.; Villinger, A. Organometallics 2010, 29, 1421. doi: 10.1021/om901063a; (b) Massey, A. G.; Park, A. J.; J. Organomet. Chem. 1964, 2, 245. doi: 10.1016/S0022 328X(00)80518 5. 27. Kolychev, E. L.; Bannenberg, T.; Freytag, M.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Chem. Eur. J. 2012, 18, 16938. doi: 10.1002/chem.201202840. 28. Hope, H. Prog. Inorg. Chem. 1994, 41, 1. doi: 10.1002/9780470166420.ch1. 29. Sheldrick, G. M. Acta. Cryst. Sect. A. 2015, 71, 3. doi: 10.1107/S2053273314026370. 30. For full details regarding crystallographic data and copies of selected NMR spectra, see the Supporting Information. CCDC 1576114Draft to 1576117 contain the supplementary crystallographic data for this paper. These data are provided free of charge by The Cambridge Crystallographic Data Centre.
16 https://mc06.manuscriptcentral.com/cjc-pubs Page 17 of 17 Canadian Journal of Chemistry
Graphical Abstract
Draft
17 https://mc06.manuscriptcentral.com/cjc-pubs