Group VI Metal Carbonyl Complexes of Bis((diphenylphosphino

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Group VI Metal Carbonyl Complexes of Bis((diphenylphosphino)methyl)diphenylborate and an Assessment of Their Utility for Template Ligand Syntheses Paul J. Fischer,* Laura Avena, Trent D. Bohrmann, Michelle C. Neary,† Grace K. Putka, and Kevin P. Sullivan‡ Department of Chemistry, Macalester College, Saint Paul, Minnesota 55105-1899, United States S Supporting Information *

ABSTRACT: Zerovalent group VI metal chemistry of anionic bis((diphenylphosphino)methyl)diphenylborate (Ph2BP2) offers some surprises in comparison to the chemistry of analogous complexes of neutral bidentate phosphines. The enhanced donor ability of Ph2BP2 relative to related bis-PPh2 ligands is confirmed by IR spectral analysis of [ASN][M(CO)4(Ph2BP2)] (ASN = 5-azoniaspiro[4.4]nonane; M = Cr, Mo, W). The mononitriles [ASN][fac-M(CO)3(RCN)(Ph2BP2)] (M = Cr, R = Me; M = Mo, R = Et; M = W, R = Et) are useful reagents for the introduction of sulfur dioxide and isocyanides to the π-basic M(CO)3(Ph2BP2) fragment. While the fundamental coordination chemistry of this anionic fragment mostly mirrors that of its conventional neutral cousins, the electronic impact of Ph2BP2 leads to divergent reactivity in some cases. For example, the sulfur dioxide complexes [ASN][mer-M(CO)3(SO2)(Ph2BP2)] (M = Mo, W) are unreactive toward CH2N2, dramatically different from the case for merM(CO)3(SO2)(L2) (L2 = dppm, dppe, dppp). The spectral data of [ASN][Mo(CO)3(CNC6H4(2-NH2))(Ph2BP2)] and [ASN][Mo(CO)3(CNCH2CH2NH2)(Ph2BP2)], salts containing the first anions of 2-aminophenyl isocyanide and 2-aminoethyl isocyanide, respectively, indicate that the anionic M(CO)3(Ph2BP2) fragment may be more useful than neutral M(CO)3(dppe) for the π-back-bonding induced stabilization of ligands prepared via template syntheses.

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INTRODUCTION The development of reliable syntheses of a family of bis(phosphino)borates, ligands similar to conventional neutral bidentate phosphines yet rendered anionic by virtue of a borate charge incorporated into the alkyl chain of the ligand backbone, has expanded the range of steric and electronic properties offered by readily accessible bidentate phosphines.1 The prototypical ligand within this family, bis((diphenylphosphino)methyl)diphenylborate, [Ph 2 B(CH2PPh2)2]− (abbreviated as Ph2BP2), has found numerous applications. The comparison of zwitterionic transition-metal Ph2BP2 complexes to their cationic analogues (containing, for example, 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), or bis((diphenylphosphino)methyl)diphenylsilane (Ph2SiP2)) is a theme of these studies. Zwitterionic charge-neutral [Ph2BP2]Pt(Me)(THF) engages benzene C−H activation faster, via an alternate mechanism, relative to [(dppp)Pt(CH3)(THF)][B(C6F5)4].2 The zwitterionic Pd(II) complex [Ph2BP2]Pd(Me)(THF) exhibits similar activity toward catalytic copolymerization of CO and ethylene to that of [(dppp)Pd(Me)(THF)][B(C6F5)4].3 The related [(Ph2BP2)Pd(THF)2][OTf] activates the C−H bond adjacent to the nitrogen atom of trialkylamines, affording η2-iminium complexes; (Ph2SiP2)Pd(OTf)2 affords similar palladacycles.4 The activity afforded by the Rh(I) © 2014 American Chemical Society

precatalyst [Ph2BP2]Rh(CH3CN)2 for hydroacylation of 4methyl-4-pentenal is markedly higher than that of [L2Rh(CH3CN)2][PF6] (L2 = dppe, dppp, Ph2SiP2), with [Ph2BP2]Rh(CH3CN)2 exhibiting higher activities for this transformation in donor solvents relative to its less tolerant cationic cousins.5 The impact of the enhanced Ph2BP2 donor capability on metal complex photophysical properties has motivated syntheses of Cu(I)6 and Ir(III)7 Ph2BP2 complexes. The stabilization of coordinatively unsaturated [Ph2BP2]Ru(BQA) (BQA = bis(8-quinolinyl)amido) highlights the versatility of Ph2BP2.8 The application of Ph2BP2 to stabilize P(I) centers within zwitterionic phosphanide metal carbonyl complexes vitally depends on the anionic borate in the ligand backbone.9 Neutral bidentate phosphines play pivotal roles in low-valent group VI metal chemistry, with metal-based reactivity often modulated via introduction of L2 with varying steric and electronic profiles. In this regard, it is striking that only one such bis(phosphino)borate complex, [ASN][Mo(CO)4(Ph2BP2)] (ASN = 5-azoniaspiro[4.4]nonane), has been prepared to date.2a While Peters spectroscopically characterized this salt to support enhanced Ph2BP2 donation to the Mo(CO)4 fragment relative to dppp and Ph2SiP2, Received: January 28, 2014 Published: February 24, 2014 1300

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[ASN][Mo(CO)4(Ph2BP2)] X-ray crystallographic characterization was not reported. As anionic Ph2BP2 is considered for group VI metal chemistry applications, further comparisons between M(CO)4 and related complexes containing conventional neutral bidentate phosphines and Ph2BP2 are necessary. Herein we report complete synthesis and characterization details for [ASN][M(CO)4(Ph2BP2)] (M = Cr, Mo, W) and compare these data to those of related M(CO)4L2 complexes. Metal-template-controlled stabilization of kinetically and thermodynamically unstable molecules at π-basic M(CO)3L2 (M = Mo, W; L2 = neutral bidentate phosphine) fragments is a useful synthetic strategy. Schenk prepared mer-M(CO)3L2{η2(S,C)-H2CSO2} via reactions of mer-M(CO)3L2(SO2) and diazomethane; the η2-CH2SO2 sulfene ligand, unknown as a free species, is stabilized via π back-bonding from the sufficiently electron rich M(CO)3L2 fragments.10 Hahn employed the fac-M(CO)3(dppe) fragment to prepare 2aminoethyl isocyanide and 2-aminophenyl isocyanide, respectively, both also unknown as free species, as ligands.11 When they are prepared on M(CO)5 fragments, these isocyanides spontaneously cyclize by intramolecular nucleophilic attack of the primary amine at the isocyanide carbon to afford Nheterocyclic carbene ligands.12 Extensive π back-bonding from the fac-M(CO)3(dppe) fragment attenuates the susceptibility of the isocyanide carbon of these 2-amino-functionalized ligands with respect to intramolecular attack. Bis(phosphino)borates seem particularly well-suited for metal-template-controlled stabilization reactions, since template-synthesized ligands are often increasingly stabilized via stronger donation from the πbasic metal fragment. To ascertain the utility of Ph2BP2 in supporting this class of reactions, we have explored the feasibility of synthesizing group VI metal carbonyl Ph2BP2 complexes containing sulfene, 2-aminophenyl isocyanide, or 2aminoethyl isocyanide.

Table 1. Infrared Carbonyl Frequencies for M(CO)4L2 in Solutiona ν(CO) (cm−1)

M(CO)4L2 Cr(CO)4(dppe) Cr(CO)4(dppp) Cr(CO)4(dppb) 1 Mo(CO)4(dppe) Mo(CO)4(dppp) Mo(CO)4(dppb) 2 W(CO)4(dppe) W(CO)4(dppp) W(CO)4(dppb) 3 a

2008, 2005, 2005, 1990, 2040, 2030, 2022, 2004, 2017, 2013, 2014, 2000,

1900, 1914, 1913, 1921, 1956, 1932, 1916, 1943, 1902, 1914, 1912, 1890,

1880 1885 1886 1882, 1932, 1906 1900, 1886, 1878 1887 1888 1877,

1874 1924, 1900 1884 1860

1855

THF solutions of 1−3; CH2Cl2 solutions of other complexes.

singlets for 1−3 in CD2Cl2 (1, δ 47.7; 2, δ 29.1; 3, δ 12.1) are nearly indistinguishable from those of their M(CO)4(dppb) analogues in CDCl3 (M = Cr, δ 46.9; M = Mo, δ 29.2; M = W, δ 12.4).14 The similarity of these resonances is unexpected and speaks to the unique nature of Ph2BP2, on the basis of the reported relationship between 31P{1H} NMR chemical shifts and chelate ring size in bis(diphenylphosphino) M(CO)4 complexes.16 In this regard, the 31P{1H} resonances of 1−3 (with six-membered chelate rings) would be expected to be upfield from those of their M(CO)3(dppb) analogues (with seven-membered chelate rings) and most similar to those of M(CO)4(dppp) (in CDCl3: M = Cr, δ 40.3; M = Mo, δ 22.3; M = W, δ 0.6).14 Complexes 1−3 were characterized by X-ray crystallography to examine whether this apparent anomaly could be rationalized via structural parameters. Thermal ellipsoid drawings depicting the mildly distorted octahedral geometries of the metal centers of 1·THF, 2, and 3·THF are displayed in Figures S1−S3 (Supporting Information), respectively. It is noteworthy that the chelate bite angles P(1)−M−P(2) of 1 (88.08(3)°), 2 (86.39(2)°), and 3 (85.68(3)°) are slightly more acute than those defining the related six-membered chelate rings of Cr(CO) 4(dppp) (89.12(2)°)17 and Mo(CO)4(dppp) (89.74(4)°).18 The bulk associated with the diphenylborate unit in the Ph2BP2 backbone (relative to the corresponding methylene unit of dppp) apparently exerts only a modest compression on this angle. The significant difference between these angles of 1−3 relative to those of M(CO)4(dppb) (M = Cr,19 93.29(5)°; M = Mo,18 91.65(4)°; M = W,19 91.75(5)°), with seven-membered bis(phosphine) chelate rings, suggests that the 31P{1H} resonances of 1−3 are not similarly related to the P(1)−M− P(2) angle as proposed in neutral M(CO)4L2 (L2 = dppm (bis(diphenylphosphino)methane), dppe, dppp, dppb).16 The molecular structures of 1−3 feature nonbonding metal−boron separations that range from 4.1 to 4.3 Å. Precursors for Metal-Template-Controlled Ligand Syntheses. Mononitrile complexes of the general formula [ASN][M(CO)3(RCN)(Ph2BP2)] were targeted as labile sources of the anionic M(CO)3(Ph2BP2) fragment. Reactions of [ASN][Ph2BP2] and M(CO)3(RCN)3 (R = Me, Et) in THF resulted in mixtures containing the desired complexes and presumed dinuclear species with μ-Ph2BP2 ligands. Fortunately, combining these reagents in nitrile solvents resulted in exclusive formation of yellow microcrystalline [ASN][fac-M(CO)3(RCN)(Ph2BP2)] (M = Cr, R = Me (4); M = Mo, R

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RESULTS AND DISCUSSION [ASN][M(CO)4(Ph2BP2)]. Straightforward ligand substitution reactions provided microcrystalline [ASN][M(CO)4(Ph2BP2)] (M = Cr (1), Mo (2), W (3)). While Mo(CO)6 seems to be the optimum precursor for 2, as reported by Peters,2a the best yields of 1 and 3 were obtained from M(CO)4(C8H12). Salts 1−3 permit further evaluation of the electronic and steric impact of anionic Ph2BP2 on the M(CO)4 fragment of group VI metals relative to conventional neutral bidentate phosphines.13 The IR ν(CO) spectral data (Table 1) support enhanced donation of Ph2BP2 toward M(CO)4 relative to dppe, dppp, and 1,4-bis(diphenylphosphino)butane (dppb).14 The highest frequency CO stretching vibration is considered to be most diagnostic of relative bidentate ligand donation in M(CO)4L2 complexes.15 These presumed a1 vibrations are significantly shifted to lower energies in 1−3 (by 14−18 cm−1) in comparison to those of the corresponding M(CO)4(dppb) complexes. The lowest energy CO vibrations of 1−3 are similarly red-shifted relative to those of M(CO)4(dppe), M(CO)4(dppp), and M(CO)4(dppb) for each metal. Increased electron-releasing character for Ph2BP2 relative to dppp has also been established via comparison of IR ν(CO) data for [Ph2BP2]Pt(Me)(CO) (2094 cm−1) and [(dppp)Pt(Me)(CO)][B(C6F5)4] (2118 cm−1).1 While Ph2BP2 is undoubtedly a stronger donor toward M(CO)4 fragments relative to dppb, 31P{1H} NMR does not discriminate among 1−3 and their corresponding M(CO)4(dppb) analogues; the chemical shifts of the 31P{1H} 1301

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Figure 1. Molecular structure of the anion of 5·THF (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): Mo−P(1) = 2.5611(6), Mo−P(2) = 2.5627(6), Mo−C(1) = 1.942(2), Mo−C(2) = 1.956(2), Mo−C(3) = 1.965(2), Mo−N(1) = 2.210(2); P(1)−Mo−P(2) = 85.105(19), P(2)−Mo−C(3) = 93.10(7), C(3)−Mo−C(1) = 84.11(9), C(1)−Mo−P(1) = 88.22(7), C(2)−Mo−C(3) = 87.36(10), C(2)−Mo−C(1) = 87.70(10), N(1)−Mo−P(2) = 83.92(5), N(1)−Mo−C(3) = 92.64(8), N(1)−Mo−P(1) = 94.91(5), C(2)−Mo−N(1) = 94.73(9), C(2)−Mo−P(1) = 94.62(7), C(1)−Mo−P(2) = 93.67(7).

= Et (5); M = W, R = Et (6)) in high yields. The IR ν(CO) and 31P{1H} NMR spectral data of 5 and 6 exhibit the same trends relative to fac-M(CO)3(EtCN)(dppp) (M = Mo, W)10 as those described above for 1−3 relative to their neutral dppp analogues. Specifically, the highest and lowest energy ν(CO) absorptions of 5 and 6 are shifted to lower energies relative to those of these dppp complexes. The 31P{1H} singlets for 5 (δ 29.1) and 6 (δ 18.7) in CD2Cl2 occur downfield from those of fac-Mo(CO) 3 (EtCN)(dppp) (δ 22.0) and fac-W(CO)3(EtCN)(dppp) (δ 7.6), respectively, in the same solvent, and are presumably similar to those of the unreported facM(CO)3(EtCN)(dppb) analogues. Salts 4−6 were characterized by X-ray crystallography; thermal ellipsoid drawings of the mildly distorted octahedral metal centers of the anions of 4, 5· THF, and 6·THF are displayed in Figure S4 (Supporting Information), Figure 1, and Figure S5 (Supporting Information), respectively. The P(1)−Mo−P(2) chelate bite angles of 4 (86.79(2)°), 5 (85.105(19)°), and 6 (85.23(3)°) are each slightly more acute (by ∼0.5−1.3°) than the corresponding angles in 1−3. The anion of 4 joins fac-Cr(CO)3(CH3CN){Ph2PN(iPr)P(Ph)NH(iPr)} as the only other structurally characterized Cr(CO)3(RCN)L2 (L = phosphine) complex.20 The anions of 5 and 6 exhibit coordination spheres similar to those of the recently structurally characterized tris(diphenylphosphino)methane complexes fac-M(CO)3(EtCN)(η2-(Ph2P)3CH) (M = Mo, W).21 Salts 4−6 are unsurprisingly excellent sources of the M(CO)3(Ph2BP2) fragment. Saturation of dichloromethane solutions of 4−6 with sulfur dioxide results in rapid RCN displacement and subsequent isomerization, affording orange [ASN][mer-M(CO)3(SO2)(Ph2BP2)] (M = Cr (7), Mo (8), W (9)) in moderate (60−75%) yields. These substitution reactions mirror those of fac-M(CO)3(EtCN)L2 (M = Mo,

W; L2 = bis(phosphine))10 in that the instantaneously formed facial isomer kinetic products completely rearrange in situ to the meridional isomer thermodynamic products. No attempts were made to isolate the facial isomers of 7−9. Exclusive isolation of meridional isomers was confirmed in solution by 31 1 P{ H} NMR spectroscopy; two doublets (that integrate to a 1:1 ratio) were observed for the diastereotopic Ph2BP2 phosphorus atoms of 7−9. The structures of 8 and 9 were probed by X-ray crystallography; thermal ellipsoid drawings that reveal the η1(S) SO2 coordination mode are displayed in Figure S6 (Supporting Information; 8) and Figure 2 (9), respectively.22 The slightly distorted octahedral W center of 9 features a P(1)−W−P(2) bite angle of 87.06(6)°; the angle that deviates most from ideality among the 12 angles that define the edges of the approximate octahedron is P(1)−W−S (100.84(2)°), enforced by steric bulk between the SO2 and the Ph2P(1) fragment. The W−S distance in 9 (2.238(2) Å) is nearly identical with the W−S distance in mer-W(CO)3(SO2)(dppe) (2.258(1) Å).10 While the differing trans influence of CO relative to that of SO2 was invoked to rationalize the statistically different W−P distances in mer-W(CO)3(SO2)(dppe) (2.525(2), 2.500(1) Å), the corresponding lengths in 9 are statistically indistinguishable (2.5281(19), 2.5252(19) Å). To confirm the anticipated utility of anionic M(CO)3(Ph2BP2) π-basic fragments to coordinate isocyanides as a prerequisite for metal-template-controlled isocyanide syntheses, nitrile substitution reactions of 5 and 6 were carried out to provide yellow microcrystalline [ASN][fac-M(CO)3(CNR)(Ph2BP2)] (R = cyclohexyl, M = Mo (10), W (11); R = 2,6-dimethylphenyl, M = Mo (12), W (13)) in moderate to high yields (65−86%). These anions are the only known complexes of general formula M(CO)3(CNR)L2 (R = cyclohexyl, 2,6-dimethylphenyl; L = phosphine). Solutions of 1302

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Figure 2. Molecular structure of the anion of 9 (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): W−S = 2.238(2), W−P(1) = 2.5281(19), W−P(2) = 2.5252(19), W−C(1) = 2.033(8), W−C(2) = 2.018(8), W−C(3) = 2.013(7); O(4)−S−O(5) = 111.7(4), P(1)−W−P(2) = 87.06(6), P(1)−W−C(3) = 82.8(2), P(2)−W−C(3) = 99.24(19), P(2)−W−C(2) = 85.3(2), P(1)−W−S = 100.84(7), S−W−C(2) = 88.7(2), S−W−C(3) = 89.9(2), S−W− C(1) = 87.8(2), C(1)−W−C(2) = 96.9(3), C(2)−W−C(3) = 86.0(3), C(1)−W−P(2) = 83.3(2), C(1)−W−P(1) = 94.7(2).

Figure 3. Molecular structure of the anion of 11·THF with the second position of the disordered cyclohexyl isocyanide group omitted for clarity (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): W(1A)−C(1A) = 1.989(4), W(1A)−C(2A) = 1.966(4), W(1A)−C(3A) = 1.964(4), W(1A)−C(4A) = 2.123(4), W(1A)− P(1A) = 2.5379(10), W(1A)−P(2A) = 2.5276(10); C(3A)−W(1A)− C(2A) = 87.00(18), C(3A)−W(1A)−C(1A) = 85.43(16), C(2A)− W(1A)−C(1A) = 90.63(16), C(3A)−W(1A)−C(4A) = 94.04(16), C(2A)−W(1A)−C(4A) = 88.87(16), C(3A)−W(1A)−P(2A) = 93.16(12), C(1A)−W(1A)−P(2A) = 92.10(12), C(4A)−W(1A)− P(2A) = 88.39(10), C(2A)−W(1A)−P(1A) = 94.97(13), C(1A)− W(1A)−P(1A) = 98.34(11), C(4A)−W(1A)−P(1A) = 82.20(11), P(2A)−W(1A)−P(1A) = 84.69(3).

10−13 contain exclusively facial isomers on the basis of IR (ν(CO) and ν(CN)) and NMR spectral data; each complex exhibits only one singlet (excluding 31P−183W satellites) in its 31 1 P{ H} spectrum in THF (10, δ 30.1; 11, δ 11.0; 12, δ 28.1; 13, δ 10.9). Salts 10 and 11 were characterized by X-ray crystallography. Isostructural 10·THF and 11·THF each feature two formula units per asymmetric unit, with noticeable disorder of the cyclohexyl isocyanide ligand in one anion but not the other. This disorder was successfully refined into two CNCy fragments with a relative occupancy of 53:47 for both 10·THF and 11·THF. Thermal ellipsoid drawings of the anions of 10· THF and 11·THF with the minor position of the disordered isocyanide ligands omitted for clarity are displayed in Figure S7 (Supporting Information) and Figure 3, respectively. The mildly distorted octahedral metal centers of the unique anions of 10 and 11 within their respective asymmetric units feature statistically indistinguishable Ph2BP2 chelate bite angles (10A, 84.59(2)°; 10B, 84.53(3)°; 11A, 84.69(3)°; 11B, 84.61(3)°) that are slightly more acute than those in related 5 and 6. Similar propionitrile substitution reactions of 5 and 6 with 2nitrophenyl isocyanide resulted in [ASN][M(CO)3(CNC6H4(2-NO2))(Ph2BP2)] (M = Mo (14), W (15)) as purple microcrystals. The enhanced π acidity of 2nitrophenyl isocyanide relative to 2,6-dimethylphenyl isocyanide results in partial isomerization of the facial isomers of 14 and 15 to the corresponding meridional isomers; infrared spectral data (both ν(CO) and ν(CN)) of reaction mixtures indicate two isomers in solution immediately after 2-nitrophenyl isocyanide addition to facial isomers 5 and 6. These infrared spectra remain unchanged for at least 16 h at ambient temperature. While equilibrium is apparently achieved very quickly at ambient temperature, the influence of temperature on the equilibria between these geometric isomers of 14 and 15, respectively, has not been investigated. It is noteworthy that Hahn did not observe analogous isomerization during the

synthesis of M(CO)3(CNC6H4(2-NO2))(dppe) from facial precursors; only facial 2-nitrophenyl isocyanide complexes were obtained.11 This difference is likely linked to the stronger donor ability of Ph2BP2 relative to that of dppe, which may increase the driving force for placing 2-nitrophenyl isocyanide trans to a Ph2BP2 phosphorus atom relative to a dppe phosphorus atom. This fac/mer isomerization is related to that of Mo(CO)3(P(OiPr)3)(dppe).23 The 31P{1H} NMR spectra of 14 and 15 in THF-d8 each exhibit two singlets (excluding 31P−183W satellites) (14, δ 29.9 (s, fac), 29.0 (s, mer); 15, δ 12.6 (s, fac), 11.9 (s, mer)) that integrate to fac:mer ratios of approximately 85:15 (14) and 70:30 (15) that remain unchanged for at least 1 week at ambient temperature. The broader 31P{1H} singlets for these isomers of 14 and 15, respectively, relative to those of the facial isomers of 10−13, and no observed doublet of doublets for the meridional isomers of 14 and 15 suggest fac/mer isomerization of these 2-nitrophenyl isocyanide complexes in THF with rates that rival the NMR time scale at ambient temperature.24 The greater Ph2BP2 donor ability relative to that of dppe is apparent via comparison of the IR ν(CN) spectral data of 14 (in Nujol; 2049, 2028 cm−1), 15 (in Nujol; 2049, 2028 cm−1), and M(CO)3(CNC6H4(2-NO2))(dppe) (in KBr; M = Mo, 2063 cm−1; M = W, 2059 cm−1).11 The distorted-octahedral metal centers of the isostructural facial anions of 14 and 15·CH3CN are displayed as thermal ellipsoid drawings in Figure 4 and Figure S8 (Supporting Information), respectively. These are the first anions containing 1303

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at −70 °C as solids; mer-W(CO)3{η2-(S,C)-H2CSO2}(dppm) was characterized by X-ray crystallography.10 The robustness of the metal−sulfene interaction was attributed to the ability of these mer-M(CO)3L2 fragments to engage the sulfene ligand in π back-bonding. The inability of the less πbasic W(CO)4(PR3) fragment to afford sulfene complexes supports this claim. In this regard, our anionic M(CO)3(Ph2BP2) fragments seemed ideal candidates to support sulfene ligands and perhaps permit the first structural characterization of a Mo sulfene. Indeed, the IR ν(CO) absorptions of 8 (in CH2Cl2; 2015 (w), 1982 (w), 1908 (s) cm−1) and 9 (in CH2Cl2; 2010 (w), 1978 (w), 1896 (s) cm−1) indicate metal centers more electron rich than in all the merM(CO)3(SO2)(L2) complexes that form stable sulfenes; the lowest energy IR ν(CO) stretching band within this set of complexes is in mer-W(CO)3(SO2)(chir) (in CH2Cl2; 2015 (w), 1949 (m), 1916 (s) cm−1).10 Surprisingly, 8 and 9 are apparently unreactive toward diazomethane. For example, CH2N2 addition to 9 (5 or 25 equiv), modeled after the procedure developed by Schenk, resulted in no color change and spectral identification of 9 as the only carbonyl complex in solution after extended reaction times. Schenk’s M(CO)3{η2(S,C)-H2CSO2}L2 syntheses proceeded essentially instantaneously upon CH2N2 addition. The sulfur centers of 8 and 9 are apparently rendered insufficiently electrophilic to react with the diazomethane; the anionic M(CO)3(Ph2BP2) fragments are too π basic to permit sulfene ligand formation. The asymmetric and symmetric IR ν(SO) stretching frequencies (in Nujol) of 8 (1202, 1063 cm−1) and 9 (1199, 1061 cm−1) are red-shifted relative to the corresponding absorptions of mer-W(CO)3(SO2)(dppe) (1224, 1065 cm−1)27 and [CpRu(SO2)(dppe)]+ (1296, 1117 cm−1).28 The last two complexes rapidly react with diazomethane to afford sulfene complexes; the lower energy ν(SO) stretching frequencies of 8 and 9 are indicative of less electrophilic η1-SO2 ligands. The inability of Ph2BP2 to support sulfene complexes analogous to mer-M(CO)3{η2(S,C)-H2CSO2}L2 provides a cautionary tale as chemistry is developed to leverage the enhanced donor capability of this anionic ligand relative to neutral bidentate phosphines. Metal-Template-Controlled Stabilization of β-Functionalized Isocyanides. Highly reactive and spectroscopically unobserved intermediates containing 2-aminoethyl isocyanide are useful precursors to NH,NH-stabilized N-heterocyclic carbene complexes.12a,29 Benzannulated N-heterocyclic carbene ligands are accessible via similarly thermodynamically unstable 2-aminophenyl isocyanide complexes.12b,c,30 Identification of πbasic metal fragments that stabilize these putative isocyanide ligands via sufficient π back-bonding to render the isocyanide carbon resistant to nucleophilic attack by the amino function informs these studies. To this end, Hahn reported inaugural examples of isolable 2-aminophenyl isocyanide and 2-aminoethyl isocyanide complexes via employment of the M(CO)3(dppe) fragment (M = Mo, W).11 The anionic Mo(CO)3(Ph2BP2) fragment also stabilizes these isocyanides in [ASN][fac-Mo(CO)3(CNC6H4(2-NH2))(Ph2BP2)] (16) and [ASN][fac-Mo(CO) 3 (CNCH 2 CH 2 NH 2 )(Ph 2 BP 2 )] (17).31 Reduction of the nitro function of 14 by Raney nickel/hydrazine hydrate provides 16 as yellow microcrystals (Scheme 1). It is noteworthy that the reaction of fac/mer isomeric mixtures of 14 exclusively affords facial 16. Propionitrile displacement from 5 by 2-azidoethyl isocyanide provides [ASN][Mo(CO)3(CNCH2CH2N3)(Ph2BP2)], which reacts via Staudinger conditions to afford 17 as tan micro-

Figure 4. Molecular structure of the anion of fac-14 (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): Mo−C(1) = 2.023(8), Mo−C(2) = 1.962(6), Mo−C(3) = 1.968(7), Mo−C(4) = 2.052(8), Mo−P(1) = 2.5587(14), Mo−P(2) = 2.5375(14), C(4)− N(1) = 1.191(9); N(1)−C(4)−Mo = 177.3(5), C(4)−N(1)−C(5) = 176.7(7), C(1)−Mo−C(2) = 85.8(3), C(1)−Mo−C(3) = 91.1(3), C(2)−Mo−C(3) = 90.2(3), C(2)−Mo−C(4) = 89.7(3), C(3)−Mo− C(4) = 89.8(3), C(3)−Mo−P(2) = 90.84(19), C(1)−Mo−P(2) = 87.69(18), C(4)−Mo−P(2) = 96.78(17), C(2)−Mo−P(1) = 94.0(2), C(1)−Mo−P(1) = 98.64(17), C(4)−Mo−P(1) = 80.79(17), P(2)− Mo−P(1) = 86.05(4).

2-nitrophenyl isocyanide, but the M−CNR distances do not definitively indicate the greater π basicity of the M(CO)3(Ph2BP2) fragment relative to the M(CO)3(dppe) fragment that is clearly communicated by the IR ν(CN) spectral data. For example, while the metal−isocyanide carbon bond length in 14 (2.052(8) Å) is 5.8σ shorter than the corresponding distance in Mo(CO)3(CNC6H4(2-NO2))(dppe) (2.098(2) Å) (consistent with the trend predicted on the basis of more extensive π back-bonding in 14), the isocyanide C−N bond distance in 14 (1.191(9) Å) is not statistically longer (by only 2.2σ) than that in Mo(CO)3(CNC6H4(2-NO2))(dppe) (1.171(2) Å).11 The differences between these metrical parameters of the tungsten analogues (15, W−C(N) = 2.062(7) Å, C−N = 1.171(9) Å; W(CO)3(CNC6H4(2NO2))(dppe), W−C(N) = 2.080(3) Å, C−N = 1.173(4) Å) are also not statistically significant.11 Metal-Template-Controlled Sulfene Ligand Stabilization. Methylene transfer from diazomethane to cationic halfsandwich ruthenium sulfur dioxide complexes [CpRu(R3P)2(η1-SO2)]+ affords the cationic sulfene complexes [CpRu(R3P)2{η2-(S,C)-H2CSO2}]+, which function as electrophiles to facilitate C−C coupling reactions with enamines and enolates. 25 Schenk showed that neutral mer-Mo(CO)3(SO2)(L2) (L2 = dppm, dppe) and mer-W(CO)3(SO2)(L2) (L2 = dppm, dppe, dppp, chir26) are sufficiently electrophilic at sulfur to react with diazomethane to provide mer-M(CO)3{η2-(S,C)-H2CSO2}L2. These W complexes are more thermally stable (with decomposition points ranging from 96 to 118 °C) than their Mo analogues, which require storage 1304

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Organometallics

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Scheme 1

Figure 5. Molecular structure of the anion of 16·THF (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): Mo−C(1) = 1.998(4), Mo−C(2) = 1.978(5), Mo−C(3) = 1.974(5), Mo−C(4) = 2.101(5), Mo−P(1) = 2.5513(11), Mo−P(2) = 2.5482(11), C(4)− N(1) = 1.165(5); N(1)−C(4)−Mo = 176.6(4), C(4)−N(1)−C(5) = 175.4(5), C(1)−Mo−C(2) = 88.51(17), C(1)−Mo−C(3) = 88.72(17), C(2)−Mo−C(3) = 92.04(19), C(2)−Mo−C(4) = 89.27(17), C(3)−Mo−C(4) = 90.83(17), C(3)−Mo−P(2) = 93.95(13), C(1)−Mo−P(2) = 82.01(12), C(4)−Mo−P(2) = 100.26(11), C(2)−Mo−P(1) = 90.77(14), C(1)−Mo−P(1) = 95.94(12), C(4)−Mo−P(1) = 84.61(12), P(2)−Mo−P(1) = 84.06(3).

crystals (Scheme 1).32 The extent of π back-bonding into the isocyanide ligands, on the basis of IR ν(CN) spectral data, is expectedly greater in 16 (in Nujol; 2069 cm−1) relative to that in M(CO)3(CN(C6H4(2-NH2))(dppe) (in KBr; M = Mo, 2097 cm−1; M = W, 2093 cm−1) and in 17 (in Nujol, 2116 cm−1) relative to that in M(CO)3(CNCH2CH2NH2)(dppe) (in KBr; M = Mo, 2133 cm−1; M = W, 2126 cm−1). Formation of the first anions containing 2-aminophenyl isocyanide and 2aminoethyl isocyanide was confirmed by X-ray crystallography; thermal ellipsoid drawings of the modestly distorted octahedral Mo centers of the anions of 16·THF and 17 are displayed in Figures 5 and 6, respectively. The most germane structural parameters to access the spectroscopically evident increased π acidity of 2-aminophenyl isocyanide in 16 relative to that in Mo(CO)3(CN(C6H4(2-NH2))(dppe) are the M−CNR distances and the CNR angles. The greater donation of Ph2BP2 relative to dppe is manifested by a statistically shorter Mo− C(4) distance in 16 (2.101(5) Å) relative to that in Mo(CO)3(CNC6H4(2-NH2))(dppe) (2.129(2) Å). The isocyanide angle in 16 (C(4)−N(1)−C(5) = 175.4(5)°) is modestly more acute than, but not statistically different from, the corresponding angle in Mo(CO)3(CNC6H4(2-NH2))(dppe) (176.0(2)°). These trends are not internally consistent upon comparison of 17 to Mo(CO)3(CNCH2CH2NH2)(dppe) (18). Statistically significant contraction of the Mo−CNR length in 17 (2.138(4) Å) relative to that in 18 (2.157(2) Å) is not concomitant with a more acute isocyanide angle in 17 (C(4)−N(1)−C(5) = 178.1(4)°) relative to that in 18

(171.4(4)°). The primacy of IR ν(CN) data relative to these metric parameters in assessing π back-bonding into isocyanide ligands has been noted.33 These spectroscopic data are consistent with both the 2-aminophenyl isocyanide and 2aminoethyl isocyanide ligands serving as stronger π-acceptor ligands in 16 and 17, respectively, relative to their electronic roles in Hahn’s dppe analogues. An assessment of the hypothesized lower susceptibilities of the Ph2BP2 complexes 16 and 17 (relative to their dppe complexes) to engage in intramolecular cyclization reactions to afford N-heterocyclic carbene complexes would be interesting to explore.

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CONCLUSION Anionic bis((diphenylphosphino)methyl)diphenylborate, a stronger donor relative to bis-PPh2 bidentate phosphines (dppe, dppp, etc.), seems generally applicable for the syntheses of more electron rich analogues of group VI metal carbonyl complexes of these neutral phosphines. While the fundamental coordination chemistry of Ph2BP2 for the anionic complexes reported herein predictably mirrors that of their neutral analogues, the Ph2BP2 electronic impact results in reactivity not always analogous to that of their neutral cousins. Application of the π-basic Mo(CO)3(Ph2BP2) fragment predictably results in an even greater degree of stabilization of 2-aminophenyl isocyanide (in 16) and 2-aminoethyl isocyanide (in 17) ligands relative to that provided by the 1305

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(app t, JCP = 4.9 Hz, ortho P(C6H5)2), 128.0 (s, meta B(C6H5)2), 127.4 (app t, JCP = 3.9 Hz, meta P(C6H5)2), 126.3 (s, para P(C6H5)2), 122.1 (s, para B(C6H5)2), 63.8 (s, br, (CH2CH2)2N), 22.5 (s, (CH2CH2)2N) ppm. [ASN][Mo(CO)4(Ph2BP2)] (2). Yield: 71%. Anal. Calcd for C54H58O5BMoNP2 (as a 1:1 THF solvate): C, 66.88; H, 6.03; N, 1.44. Found: C, 66.35; H, 5.88; N, 1.45. Mp: 184−185 °C dec. IR (THF): ν(CO) 2004 (m), 1943 (w), 1886 (s), 1860 (m) cm−1. IR (Nujol): ν(CO) 2070 (w), 2001 (s), 1946 (w), 1870 (s), 1835 (s, sh) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 29.1 (s) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 219.9 (m, COeq), 213.3 (t, 2JPC = 9.0 Hz, COax), 143.1 (m, ipso P(C6H5)2), 133.1 (s, ortho B(C6H5)2), 132.7 (app t, JCP = 5.9 Hz, ortho P(C6H5)2), 127.9 (s, meta B(C6H5)2), 127.5 (app t, JCP = 3.9 Hz, meta P(C6H5)2), 126.2 (s, para P(C6H5)2), 122.1 (s, para B(C6H5)2), 63.8 (m, (CH2CH2)2N), 22.5 (s, (CH2CH2)2N) ppm. [ASN][W(CO) 4(Ph 2BP2)] (3). Yield: 85%. Anal. Calcd for C54H58O5BNP2W (as a 1:1 THF solvate): C, 61.32; H, 5.53; N, 1.32. Found: C, 61.63; H, 5.70; N, 1.31. Mp: 218−220 °C dec. IR (THF): ν(CO) 2000 (m), 1890 (m, sh), 1877 (s), 1855 (m) cm−1. IR (Nujol): ν(CO) 1999 (m), 1875 (s), 1844 (s, sh) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 12.1 (s, 31P−183W satellites: 13.0, 11.2, J = 209 Hz) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 211.3 (m, COeq), 206.3 (m, COax), 142.5 (m, ipso P(C6H5)2), 133.1 (s, ortho B(C6H5)2), 132.8 (app t, JCP = 5.9 Hz, ortho P(C6H5)2), 128.2 (s, meta B(C6H5)2), 127.5 (app t, JCP = 3.9 Hz, meta P(C6H5)2), 126.3 (s, para P(C6H5)2), 122.2 (s, para B(C6H5)2), 63.8 (m, (CH2CH2)2N), 22.5 (s, (CH2CH2)2N) ppm. [ASN][fac-Cr(CO)3(CH3CN)(Ph2BP2)] (4). Yield: 64%. Anal. Calcd for C51H53O3BCrN2P2: C, 70.67; H, 6.16; N, 3.23. Found: C, 71.16; H, 6.38; N, 3.17. Mp: 188−190 °C dec. IR (CH3CN) ν(CO) 1904 (s), 1798 (m), 1779 (s, sh) cm−1. IR (Nujol): ν(CO) 1994 (w), 1899 (s), 1832 (w) cm−1. 31P{1H} NMR (121 MHz, CD3CN): δ 47.1 (s) ppm. 13C{1H} NMR (75 MHz, CD3CN): δ 233.5 (app t, JCP = 5.8 Hz, COeq), 231.9 (t, JCP = 13.6 Hz, COax), 144.2 (app t, JCP = 15.6 Hz, ipso P(C6H5)2), 143.6 (app t, JCP = 8.8 Hz, ipso P(C6H5)2), 133.5−133.9 (m, ortho B(C6H5)2 and P(C6H5)2), 127.7−128.0 (m, meta B(C6H5)2 and P(C6H5)2), 127.0 (s, para P(C6H5)2), 126.4 (s, para P(C6H5)2), 122.8 (s, para B(C6H5)2), 122.3 (s, para B(C6H5)2), 63.8 (m, (CH 2 CH 2 ) 2 N), 23.3 (m, Ph 2 B(CH 2 PPh 2 ) 2 ), 22.7 (s, br, (CH2CH2)2N) ppm. C-13 resonances for coordinated CH3CN were not observed, mostly likely due to rapid CD3CN exchange. [ASN][fac-Mo(CO)3(CH3CH2CN)(Ph2BP2)] (5). CH3CH2CN (80 mL) was added to Mo(CO)3(CH3CH2CN)3 (1.000 g, 2.900 mmol) and [ASN][Ph2BP2] (2.000 g, 2.900 mmol). The solution was stirred (2 h) and subsequently filtered through alumina. Removal of the solvent in vacuo resulted in a yellow oil. The addition of Et2O (60 mL) resulted in a sticky solid that was rendered a powder by trituration. This solid was isolated by filtration, washed with Et2O (4 × 10 mL), and dried in vacuo. Et2O diffusion into a CH3CN solution provided yellow microcrystals (2.38 g, 89%). Anal. Calcd for C52H55O3BMoN2P2: C, 67.54; H, 6.00; N, 3.03. Found: C, 68.02; H, 6.34; N, 2.93. Mp: 71−74 °C dec. IR (CH3CH2CN): ν(CO) 1913 (s), 1808 (m), 1794 (m, sh) cm−1. IR (Nujol): ν(CO) 1904 (s), 1797 (s, sh), 1771 (s) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 29.1 (s) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 217.5 (m, COeq), 217.3 (app t, J = 5.9 Hz, COax), 143.0 (m, ipso P(C6H5)2), 141.7 (m, ipso P(C6H5)2), 133.1−133.5 (m, ortho B(C6H5)2) and P(C6H5)2), 127.7 (s, CH3CH2CN), 127.2−127.4 (m, meta B(C6H5)2 and P(C6H5)2), 126.5 (s, para P(C6H5)2), 125.9 (s, para P(C6H5)2), 122.4 (s, para B(C6H5)2), 121.9 (s, para B(C6H5)2), 63.6 (m, (CH2CH2)2N), 22.5 (m, Ph2 B(CH2PPh2 )2 ), 22.4 (s, br, (CH2CH2) 2N), 15.6 (s, CH3CH2CN), 12.6 (s, CH3CH2CN) ppm. [ASN][fac-W(CO)3(CH3CH2CN)(Ph2BP2)] (6). Yield: 80%. Anal. Calcd for C52H55O3BN2P2W: C, 61.68; H, 5.47; N, 2.77. Found: C, 61.98; H, 5.92; N, 2.86. Mp: 97−99 °C dec. IR (CH3CH2CN) ν(CO) 1906 (s), 1800 (s) cm−1. IR (Nujol): ν(CO) 1898 (s), 1789 (s, sh), 1766 (s) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 18.7 (s, 31 P−183W satellites: 19.9, 17.9, J = 219 Hz) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 225.6 (app t, JCP = 3.6 Hz, COax), 223.6 (m, COeq),

Figure 6. Molecular structure of the anion of 17 (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): Mo−C(1) = 1.951(4), Mo−C(2) = 1.971(4), Mo−C(3) = 1.977(4), Mo−C(4) = 2.138(4), Mo−P(1) = 2.5487(11), Mo−P(2) = 2.5277(11), C(4)− N(1) = 1.161(5); N(1)−C(4)−Mo = 174.4(3), C(4)−N(1)−C(5) = 178.1(4), C(1)−Mo−C(2) = 89.72(17), C(1)−Mo−C(3) = 88.36(17), C(2)−Mo−C(3) = 88.44(16), C(1)−Mo−C(4) = 91.98(16), C(2)−Mo−C(4) = 86.08(15), C(1)−Mo−P(2) = 89.27(13), C(3)−Mo−P(2) = 90.05(12), C(4)−Mo−P(2) = 95.44(11), C(2)−Mo−P(1) = 97.08(13), C(3)−Mo−P(1) = 97.70(12), C(4)−Mo−P(1) = 82.62(10), P(2)−Mo−P(1) = 84.08(3).

Mo(CO)3dppe fragment. However, the dramatic inertness of 8 and 9 toward diazomethane relative to M(CO)3(SO2)(L2) (L2 = dppm, dppe, dppp, chir) and apparently different fac/mer isomerization barriers of 14 and 15 relative to those of M(CO)3(CNC6H4(2-NO2))(dppe) highlight the surprises that Ph2BP2 may offer in tuning the reactivity of low-valent group VI metal complexes. Efforts to uncover more novel properties engendered by Ph2BP2 are underway in this laboratory.

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EXPERIMENTAL SECTION

Similar procedures were conducted to synthesize 1−3, 4−6, 7−9, and 10−15. Representative procedures for 1, 5, 8, and 10 are provided below. General procedures and complete characterization details (including 1H NMR spectral data) are given in the Supporting Information. [ASN][Cr(CO)4(Ph2BP2)] (1). THF (40 mL) was added to [ASN][Ph2BP2] (0.500 g, 0.725 mmol) and Cr(CO)4(C8H12) (0.197 g, 0.725 mmol). The orange solution was refluxed (16 h) and subsequently filtered through Celite. Most of the solvent from the resulting yellow solution was removed in vacuo. Addition of Et2O (40 mL) affected the precipitation of a yellow powder that was isolated by filtration, washed with Et2O (3 × 10 mL), and dried in vacuo. Pentane diffusion into a THF solution provided pale yellow microcrystals (0.551 g, 89%). Anal. Calcd for C54H58O5BCrNP2 (as a 1:1 THF solvate): C, 70.06; H, 6.31; N, 1.51. Found: C, 70.10; H, 6.41; N, 1.42. Mp: 194−195 °C dec. IR (THF): ν(CO) 1990 (m), 1892 (s), 1875 (s), 1855 (s) cm−1. IR (Nujol): ν(CO) 1990 (s), 1921 (m), 1882 (s), 1874 (s, sh), 1844 (s), 1827 (s) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 47.7 (s) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 230.2 (app t, 2JCP = 9.7 Hz, COeq), 224.3 (t, 2JCP = 13.7 Hz, COax), 143.2 (app t, JCP = 15.6 Hz, ipso P(C6H5)2), 133.0 (s, ortho B(C6H5)2), 132.7 1306

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Organometallics

Article

143.6 (m, ipso P(C6H5)2), 142.5 (m, ipso P(C6H5)2), 133.2−133.4 (m, ortho P(C6H5)2 and B(C6H5)2), 128.0 (s, meta B(C6H5)2), 127.9 (s, meta B(C6H5)2), 127.6 (s, CH3CH2CN), 127.1−127.4 (m, meta P(C6H5)2), 126.5 (s, para P(C6H5)2), 126.0 (s, para P(C6H5)2), 122.4 (s, para B(C6H5)2), 121.9 (s, para B(C6H5)2), 63.7 (s, br, (CH2CH2)2N), 22.5 (m, Ph2B(CH2Ph2)2), 22.5 (s, (CH2CH2)2N), 15.7 (s, CH3CH2CN), 12.6 (s, CH3CH2CN) ppm. [ASN][mer-Cr(CO)3(SO2)(Ph2BP2)] (7). Yield: 74%. Anal. Calcd for C49H50BCrNO5P2S: C, 66.15; H, 5.66; N, 1.57. Found: C, 65.90; H, 5.79; N, 2.68. IR (CH3CN): ν(CO) 2001 (w), 1901 (s) cm−1; ν(SO) 1066 (m) cm−1. IR (Nujol): ν(CO) 2009 (m), 1924 (m, sh), 1910 (s, sh), 1890 (s), 1869 (m, sh) cm−1; ν(SO) 1059 (m) cm−1. 31 1 P{ H} NMR (121 MHz, CD3CN): δ 48.7 (d, 2JPP = 44.1 Hz), 41.1 (d, 2JPP = 44.7 Hz) ppm. 13C{1H} NMR (75 MHz, CD3CN): δ 230.4 (m, COeq), 220.7 (app t, JCP = 13.7 Hz, COax), 140.8 (d, JCP = 33.2 Hz, ipso P(C6H5)2), 139.7 (d, JCP = 33.2 Hz, ipso P(C6H5)2), 132.3 (s, ortho B(C6H5)2), 131.3−131.4 (m, ortho P(C6H5)2), 128.3 (m, meta B(C6H5)2), 127.3−127.4 (m, meta P(C6H5)2), 125.7 (s, para P(C6H5)2), 121.7 (s, para B(C6H5)2), 61.9 (s, (CH2CH2)2N), 21.7 (m, Ph2B(CH2Ph2)2), 21.6 (s, (CH2CH2)2N) ppm. [ASN][mer-Mo(CO)3(SO2)(Ph2BP2)] (8). CH2Cl2 (20 mL) was added to 5 (0.462 g, 0.500 mmol), and the yellow solution was cooled to 0 °C. The solution became red-orange upon its saturation in SO2 and was stirred at ambient temperature (8 h). Removal of volatiles in vacuo (trap-to-trap transfer) resulted in an orange solid to which CH2Cl2 (60 mL) was added. An orange solution was obtained by filtration through Celite that was subsequently concentrated in vacuo. Addition of Et2O (60 mL) resulted in a pale orange powder that was isolated via filtration, washed with Et2O (3 × 15 mL), and dried in vacuo. Et2O diffusion into a CH3CN solution provided pale yellow microcrystals (0.292 g, 63%). Anal. Calcd for C49H50O5BMoNP2S: C, 63.03; H, 5.40; N, 1.50. Found: C, 62.70; H, 5.54; N, 1.43. Mp: 164− 165 °C dec. IR (CH2Cl2): ν(CO) 2015 (w), 1982 (w), 1908 (s) cm−1; ν(SO) 1060 (m) cm−1. IR (Nujol): ν(CO) 2022 (m), 1984 (w), 1936 (m, sh), 1920 (s), 1897 (s, sh), 1871 (m, sh) cm−1; ν(SO) 1202 (w), 1063 (m) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 32.9 (d, 2JPP = 33.0 Hz), 26.0 (d, 2JPP = 33.0 Hz) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 218.0 (dd, 2JCP(trans) = 23.1 Hz, 2JCP(cis) = 13.6 Hz, COeq), 209.6 (app t, JCP = 8.8 Hz, COax), 140.6 (d, JCP = 33.2 Hz, ipso P(C6H5)2), 139.8 (d, JCP = 35.2 Hz, ipso P(C6H5)2), 132.2 (s, ortho B(C6H5)2), 131.3−131.5 (m, ortho P(C6H5)2), 128.4 (s, meta B(C6H5)2), 128.2 (s, meta B(C6H5)2), 127.4−127.5 (m, meta P(C6H5)2), 125.6 (s, para P(C6H5)2), 121.7 (s, para B(C6H5)2), 61.8 (s, (CH2CH2)2N), 21.2 (s, (CH2CH2)2N) ppm. [ASN][mer-W(CO)3(SO2)(Ph2BP2)] (9). Yield: 69%. Anal. Calcd for C49H50O5BNP2SW: C, 57.61; H, 4.93; N, 1.37. Found: C, 57.61; H, 5.08; N, 1.34. Mp: 168−169 °C dec. IR (CH2Cl2): ν(CO) 2010 (w), 1978 (w), 1896 (s) cm−1; ν(SO) 1059 (m) cm−1. IR (Nujol): ν(CO) 2016 (m), 1981 (w), 1957 (w), 1929 (m, sh), 1911 (s, sh), 1888 (s), 1866 (m, sh) cm−1; ν(SO) 1199 (w), 1061 (m) cm−1. 31P{1H} NMR (121 MHz, CD2Cl2): δ 14.0 (d, 2JPP = 25.2 Hz, 31P−183W satellites: 15.0, 14.8, 13.1, 12.9, J = 233 Hz, 2JPP = 24.3 Hz), 10.9 (d, 2JPP = 24.6 Hz, 31P−183W satellites: 11.9, 11.7, 10.0, 9.8, J = 227 Hz, 2JPP = 24.8 Hz) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 209.2 (m, COeq), 203.1 (m, COax), 140.2 (d, JCP = 38.1 Hz, ipso P(C6H5)2), 139.4 (d, JCP = 40.0 Hz, ipso P(C6H5)2), 132.2 (s, ortho B(C6H5)2), 131.4−131.6 (m, ortho P(C6H5)2), 128.6 (s, meta B(C6H5)2), 128.5 (s, meta B(C6H5)2), 127.5 (s, meta P(C6H5)2), 127.3 (s, meta P(C6H5)2), 125.6 (s, para P(C6H5)2), 121.7 (s, para B(C6H5)2), 61.8 (s, (CH2CH2)2N), 21.6 (s, (CH2CH2)2N) ppm. [ASN][fac-Mo(CO)3(CNC6H11)(Ph2BP2)] (10). THF (30 mL) was added to 5 (0.300 g, 0.324 mmol). An aliquot (1 mL) of a cyclohexyl isocyanide stock solution (1.053 g of C6H11NC in 27.0 mL of CH2Cl2; 1 mL contains 0.357 mmol of C6H11NC) was added dropwise. The solution turned from bright yellow to colorless upon stirring (1 h). The solution was filtered through Celite and concentrated to ∼6 mL in vacuo. Addition of Et2O (35 mL) resulted in the precipitation of a white powder that was isolated by filtration, washed with Et2O (3 × 10 mL), and dried in vacuo. Et2O diffusion into a THF solution provided pale yellow needles (0.236 g, 74%). Anal. Calcd for

C56H61BMoN2O3P2 (as a 1:1 THF solvate): C, 68.57; H, 6.62; N, 2.67. Found: C, 68.24; H, 6.98; N, 2.45. Mp: 178−179 °C. IR (THF): ν(CO) 1916 (s), 1828 (s) cm−1, ν(CN) 2116 (w) cm−1. IR (Nujol): ν(CO) 1914 (m), 1826 (m, sh), 1813 (m, sh), 1793 (m) cm−1; ν(CN) 2144 (w), 2125 (w, sh) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 30.1 (s) ppm. 13C{1H} NMR (101 MHz, THF-d8): δ 222.1 (m, COeq), 219.6 (app t, JCP = 8.7 Hz, COax), 166.0 (m, NC), 144.0 (m, ipso P(C6H5)2), 133.0 (s, br, ortho B(C6H5)2), 132.5 (m, ortho P(C6H5)2), 126.2 (m, meta P(C6H5)2 and meta B(C6H5)2), 125.2 (s, para P(C6H5)2), 125.1 (s, para P(C6H5)2), 121.0 (s, para B(C6H5)2), 120.8 (s, para B(C6H5)2), 62.7 (m, (CH2CH2)2N), 53.2 (s, C6H11), 32.6 (s, C6H11), 25.1 (s, C6H11), 23.1 (s, C6H11), 21.8 (s, (CH2CH2)2N) ppm. [ASN][fac-W(CO)3(CNC6H11)(Ph2BP2)] (11). Yield: 65%. Anal. Calcd for C60H69BWN2O4P2 (as a 1:1 THF solvate): C, 63.28; H, 6.11; N, 2.46. Found: C, 63.09; H, 6.46; N, 2.32. Mp: 203−205 °C dec. IR (THF): ν(CO) 1908 (s), 1822 (s) cm−1; ν(CN) 2112 (w) cm−1. IR (Nujol): ν(CO) 1912 (s), 1823 (s, sh), 1796 (s) cm−1; ν(CN) 2116 (m) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 11.0 (s, 31 P−183W satellites: 11.6, 10.4, J = 211 Hz) ppm. 13C{1H} NMR (101 MHz, THF-d8): δ 212.1 (m, COeq), 210.4 (app t, JCP = 6.8 Hz, COax), 157.4 (m, NC), 141.6 (m, ipso P(C6H5)2), 131.1 (s, ortho B(C6H5)2), 130.7 (m, ortho P(C6H5)2), 124.62 (s, meta B(C6H5)2), 124.55 (s, meta B(C6H5)2), 124.3 (m, meta P(C6H5)2), 123.3 (s, para P(C6H5)2), 123.2 (s, para P(C6H5)2), 119.2 (s, para B(C6H5)2), 119.0 (s, para B(C6H5)2), 60.9 (m, (CH2CH2)2N), 51.5 (s, C6H11), 30.8 (s, C6H11), 21.6 (s, C6H11), 21.3 (s, C6H11), 19.9 (s, (CH2CH2)2N) ppm. [ASN][fac-Mo(CO)3(CNC6H3(2,6-CH3))(Ph2BP2)] (12). Yield: 85%. Anal. Calcd for C58H59BN2O3P2Mo: C, 69.61; H, 5.94; N, 2.80. Found: C, 70.13; H, 6.37; N, 2.60. Mp: 249−251 °C. IR (THF): ν(CO) 1912 (s), 1837 (s) cm−1; ν(CN) 2056 (w) cm−1. IR (Nujol): ν(CO) 1902 (s), 1836 (m, sh), 1813 (s) cm−1; ν(CN) 2063 (m), 2002 (w, sh) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 28.1 (s) ppm. 13 C{1H} NMR (101 MHz, THF-d8): δ 219.7 (m, COeq), 217.3 (app t, JCP = 8.6 Hz, COax), 180.6 (app t, J = 10.3 Hz, CN), 163.8 (m, ipso B(C6H5)2), 141.6 (m, ipso P(C6H5)2), 132.7 (s, para CNC6H3(2,6Me)), 131.0 (s, ortho B(C6H5)2), 130.9 (s, ortho B(C6H5)2), 130.6 (m, ortho P(C6H5)2), 127.7 (s, ipso CNC6H3(2,6-Me)), 125.2 (s, meta B(C6H5)2), 124.5 (s, meta CNC6H3(2,6-Me)), 124.4 (m, meta P(C6H5)2), 124.1 (s, ortho CNC6H3(2,6-Me)), 123.4 (s, para P(C6H5)2), 123.2 (s, para P(C6H5)2), 119.1 (s, para B(C6H5)2), 118.9 (s, para B(C6H5)2), 60.8 (m, (CH2CH2)2N), 19.9 (s, (CH2CH2)2N), 16.7 (s, CNC6H3(2,6-Me)) ppm. [ASN][fac-W(CO)3(CNC6H3(2,6-CH3))(Ph2BP2)] (13). Yield: 86%. Anal. Calcd for C58H59BN2O3P2W: C, 63.99; H, 5.46; N, 2.57. Found: C, 64.56; H, 5.65; N, 2.37. Mp: 230−233 °C dec. IR (THF): ν(CO) 1904 (s), 1832 (s) cm−1; ν(CN) 2050 (w) cm−1. IR (Nujol): ν(CO) 1893 (s), 1828 (m, sh), 1808 (s) cm−1; ν(CN) 2054 (m) cm−1. 31 1 P{ H} NMR (162 MHz, THF-d8): δ 10.9 (s, 31P−183W satellites: 11.5, 10.2, J = 212 Hz) ppm. 13C{1H} NMR (101 MHz, THF-d8): δ 214.2 (m, COeq), 213.2 (app t, JCP = 6.7 Hz, COax), 176.8 (app t, J = 9.2 Hz, CN), 166.5 (m, ipso B(C6H5)2), 143.8 (m, ipso P(C6H5)2), 135.5 (s, para CNC6H3(2,6-Me)), 133.8 (s, ortho B(C6H5)2), 133.7 (s, ortho B(C6H5)2), 133.4 (m, ortho P(C6H5)2), 130.9 (s, ipso CNC6H3(2,6-Me)), 128.0 (s, meta CNC6H3(2,6-Me)), 127.54 (s, meta B(C6H5)2), 127.50 (s, ortho CNC6H3(2,6-Me)), 127.2 (m, meta P(C6H5)2), 126.2 (s, para P(C6H5)2), 126.1 (s, para P(C6H5)2), 122.0 (s, para B(C 6 H 5 ) 2 ), 121.7 (s, para B(C 6 H 5 ) 2 ), 63.6 (m, (CH2CH2)2N), 22.7 (s, (CH2CH2)2N), 19.6 (s, CNC6H3(2,6-Me)) ppm. [ASN][Mo(CO)3(CNC6H4(2-NO2))(Ph2BP2)] (14). Yield: 87%. Anal. Calcd for C60H62BMoN3O6P2 (as a 1:1 THF solvate): C, 66.12; H, 5.73; N, 3.86. Found: C, 66.47; H, 5.74; N, 3.80. Mp: 153− 155 °C dec. IR (THF): ν(CO) 2004 (w) 1907 (s), 1870 (m, sh), 1851 (m, sh) cm−1; ν(CN) 2046 (w), 2021 (w, sh) cm−1. IR (Nujol): ν(CO) 1897 (s), 1857 (m), 1830 (s) cm−1; ν(CN) 2049 (m), 2028 (w, sh) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 29.9 (s, fac), 29.0 (s, mer) ppm. The fac:mer ratio on the basis of these peak areas was ∼85:15. The mer isomer concentration was sufficiently low that only C-13 resonances assigned to the fac isomer are reported. 13C{1H} 1307

dx.doi.org/10.1021/om5001056 | Organometallics 2014, 33, 1300−1309

Organometallics

Article

NMR (101 MHz, THF-d8): δ 220.7 (m, COeq), 217.4 (m, COax), 143.2 (m, ipso P(C6H5)2), 142.0 (s, C-2, CNC6H4(2-NO2)), 133.6 (s, C-5, CNC6H4(2-NO2)), 133.0 (s, ortho B(C6H5)2), 132.9 (s, ortho B(C6H5)2), 132.5 (app t, J = 5.8 Hz, ortho P(C6H5)2), 132.3 (app t, J = 5.8 Hz, ortho P(C6H5)2), 130.8 (s, C-6, CNC6H4(2-NO2)), 126.7 (s, C-4, CNC6H4(2-NO2)), 126.49 (s, meta P(C6H5)2), 126.45 (s, meta B(C6H5)2), 126.39 (s, meta P(C6H5)2), 126.3 (s, meta B(C6H5)2), 125.3 (s, para B(C6H5)2), 125.2 (s, br, para P(C6H5)2), 125.1 (s, br, para P(C6H5)2), 124.7 (s, para B(C6H5)2), 120.89 (s, C-3, CNC6H4(2NO2)), 120.85 (s, C-1, CNC6H4(2-NO2)), 62.7 (m, (CH2CH2)2N), 22.2 (s, Ph2B(CH2PPh2)2), 21.8 (s, (CH2CH2)2N) ppm. [ASN][W(CO)3(CNC6H4(2-NO2))(Ph2BP2)] (15). Yield: 88%. Anal. Calcd for C60H62BMoN3O6P2 (as a 1:1 THF solvate): C, 61.17; H, 5.31; N, 3.57. Found: C, 61.24; H, 5.58; N, 3.55. Mp: 149−151 °C dec. IR (THF): ν(CO) 2000 (w), 1899 (s), 1876 (s, sh), 1854 (s, sh) cm−1; ν(CN) 2047 (w, sh), 2022 (w, sh) cm−1. IR (Nujol): ν(CO) 1897 (s), 1857 (m), 1830 (s) cm−1; ν(CN) 2049 (m), 2028 (w, sh) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 12.6 (s, 31P−183W satellites: 13.2, 11.9, J = 215 Hz, fac), 11.9 (s, 31P−183W satellites: 12.5, 11.2, J = 219 Hz, mer) ppm. The fac:mer ratio on the basis of these peak areas was ∼70:30. The mer isomer concentration was sufficiently low that only C-13 resonances assigned to the fac isomer are reported, with the exception of the 13CO resonances. 13C{1H} NMR (101 MHz, THF-d8): δ 212.4 (m, fac, COeq), 210.6 (m, fac, COax), 209.9 (m, mer, COeq), 205.6 (m, mer, COax), 190.4 (m, CN), 142.5 (m, ipso P(C6H5)2), 141.9 (s, C-2, CNC6H4(2-NO2)), 133.6 (s, C-5, CNC6H4(2-NO2)), 132.8 (m, ortho B(C6H5)2), 132.4 (m, ortho P(C6H5)2), 130.7 (s, C-6, CNC6H4(2-NO2)), 127.0 (s, C-4, CNC6H4(2-NO2)), 126.8 (s, meta B(C6H5)2), 126.7 (s, meta B(C6H5)2), 126.5 (app t, J = 4.6 Hz, meta P(C6H5)2), 125.2 (s, br, para P(C6H5)2), 124.9 (s, para B(C6H5)2), 124.8 (s, para B(C6H5)2), 121.02 (s, C-3, CNC6H4(2-NO2)), 120.99 (s, C-1, CNC6H4(2-NO2)), 62.7 (m, (CH2CH2)2N), 21.8 (s, (CH2CH2)2N) ppm. [ASN][fac-Mo(CO)3(CNC6H4(2-NH2))(Ph2BP2)] (16). A slurry of aqueous Raney nickel (∼0.5 mL, estimated on the tip of a spatula) was added to a solution of 14 (0.600 g, 0.588 mmol) in THF (40 mL). The suspension was cooled to 0 °C prior to addition of hydrazine hydrate (0.600 mL of 50−60% hydrazine hydrate solution). The solution was removed from the ice bath and stirred (105 min). The color changed from dark purple to yellow within 30 min. The suspension was filtered through Celite, and the yellow filtrate was concentrated to ∼4 mL in vacuo. The addition of Et2O (35 mL) resulted in the precipitation of a yellow solid that was isolated by filtration, washed with Et2O (3 × 15 mL), and dried in vacuo. Et2O diffusion into a THF solution provided yellow needles (0.438 g, 74%) Anal. Calcd for C60H64BMoN3O4P2 (as a 1:1 THF solvate): C, 67.99; H, 6.09; N, 3.96. Found: C, 68.06; H, 6.16; N, 3.71. Mp: 213−214 °C dec. IR (THF): ν(CO) 1914 (s), 1835 (m) cm−1; ν(CN) 2068 (w) cm−1. IR (Nujol): ν(CO) 1911 (m), 1840 (m, sh), 1818 (m) cm−1; ν(CN) 2069 (w) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 27.9 (s) ppm. 1H NMR (400 MHz, THF-d8): δ 7.36−7.42 (m, 8H, ortho P(C6H5)2), 6.97 (m, 2H, ortho B(C6H5)2), 6.83−6.94 (m, 14H, ortho B(C6H5)2, meta P(C6H5)2, meta B(C6H5)2), 6.72 (dd, J = 7.9 Hz, J = 1.4 Hz, 1H, H-4, CNC6H4(2-NH2)), 6.62 (dd, 8.2 Hz, J = 1.1 Hz, 1H, H-3, CNC6H4(2-NH2)), 6.42−6.60 (m, 8H, para P(C6H5)2, para B(C6H5)2, H-5/6 CNC6H4(2-NH2)), 4.31 (s, 2H, NH2), 3.15 (m, 8H, (CH 2 CH 2 ) 2 N), 1.93 (m, br, 12H, Ph 2 B(CH 2 PPh 2 ) 2 and (CH2CH2)2N) ppm. Varying quantities of THF (with one molecule per formula unit the maximum) were observed in samples of 16. 13 C{1H} NMR (101 MHz, THF-d8): δ 219.7 (m, COeq), 216.9 (app t, J = 8.8 Hz, COax), 179.4 (app t, J = 11.0 Hz, CN), 142.2 (s, C-2, CNC6H4(2-NH2)), 141.8 (m, ipso P(C6H5)2), 131.2 (s, ortho B(C6H5)2), 131.1 (s, ortho B(C6H5)2), 130.5 (m, ortho P(C6H5)2), 125.7 (s, C-4, CNC6H4(2-NH2)), 124.4−124.6 (m, meta P(C6H5)2 and meta B(C6H5)2), 123.8 (s, C-4, CNC6H4(2-NH2)), 123.4 (s, para P(C6H5)2), 123.2 (s, para P(C6H5)2), 119.1 (s, para B(C6H5)2), 119.0 (s, para B(C6H5)2), 114.2 (s, C-3, CNC6H4(2-NH2)), 113.7 (s, C-1, CNC6H4(2-NH2)), 112.5 (s, C-5, CNC6H4(2-NH2)), 60.8 (m, (CH2CH2)2N), 19.9 (s, (CH2CH2)2N) ppm.

[ASN][fac-Mo(CO)3(CNCH2CH2NH2)(Ph2BP2)] (17). An aliquot (2.0 mL) of a 2-azidoethyl isocyanide stock solution in CH2Cl2 (stock solution composition: 0.4825 g of CNCH2CH2N3 in 14.0 mL of CH2Cl2; 2 mL delivers 0.714 mmol of isocyanide) was added to a solution of 5 (0.600 g, 0.648 mmol) in THF (40 mL). The mixture was stirred for 1 h. An infrared spectrum of the solution indicated complete consumption of 5 and formation of [ASN][Mo(CO)3(CNCH2CH2N3)(Ph2BP2)] (IR (THF): ν(CO) 1920 (s), 1832 (m); ν(CN) 2120 (w), ν(N3) 2098 (w) cm−1). The solution was filtered through Celite, and the filtrate was concentrated to ∼5 mL. The addition of Et2O (40 mL) resulted in an oily brown precipitate. The Et2O-rich mother liquor was removed via cannula, and more Et2O (40 mL) was added. The mixture was stirred (1 h) before the solvent was removed via cannula. Upon drying in vacuo (15 min) the residue changed to a tan powder that was subsequently dissolved in THF (40 mL). An aliquot (2.0 mL) of a stock solution of PMe3 in THF (stock solution composition 1.0 mL of PMe3 in 24.0 mL of THF; 2 mL delivers 0.778 mmol of PMe3) was added, and the solution was stirred (5 h). An IR spectrum (IR (THF): ν(CO) 1917 (s), 1827 (m); ν(CN) 2128 (w) cm−1) indicated complete consumption of the azido complex to afford a presumed iminophosphorane intermediate. Degassed H2O (0.15 mL) was added, and the solution was stirred for 10 h. The solution (IR (THF): ν(CO) 1919 (s), 1827 (m); ν(CN) 2119 cm−1) was filtered through Celite and concentrated to ∼5 mL in vacuo. The addition of Et2O (35 mL) resulted in a brown oil. The mother liquor was removed via cannula, and Et2O was added (40 mL). The oil changed to a tan powder with stirring (2 h). This solid was isolated by filtration, washed with Et2O (3 × 10 mL) and dried in vacuo. Et2O diffusion into a THF solution provided tan microcrystals (0.434 g, 71%). Anal. Calcd for C56H64BMoN3O4P2 (as a 1:1 THF solvate): C, 66.47; H, 6.38; N, 4.15. Found: C, 66.53; H, 6.48; N, 3.90. Mp: 185−187 °C. IR (THF): ν(CO) 1918 (s), 1829 (s) cm−1; ν(CN) 2119 (w) cm−1. IR (Nujol): ν(CO) 1914 (s), 1835 (m, sh), 1791 (s) cm−1; ν(CN) 2116 (m) cm−1. 31P{1H} NMR (162 MHz, THF-d8): δ 30.4 (s) ppm. 1H NMR (400 MHz, THF-d8): δ 7.38−7.41 (m, 8H, ortho P(C6H5)2), 7.01 (m, 2H, ortho B(C6H5)2), 6.80−6.94 (m, 14H, ortho B(C6H5)2, meta P(C6H5)2, meta B(C6H5)2), 6.66 (app t, J = 5.8 Hz, 2H, para P(C6H5)2), 6.57 (app t, J = 7.1 Hz, 1H, para B(C6H5)2), 6.48 (app t, J = 6.8 Hz, 2H, P(C6H5)2), 6.41 (app t, J = 7.0 Hz, 1H, B(C6H5)2), 3.12 (m, 10H, (CH2CH2)2N and CNCH2), 2.54 (t, J = 6.0 Hz, 2H, CH2NH2), 1.96 (s, br, 4H, Ph2B(CH2PPh2)2), 1.91 (m, 8H, (CH2CH2)2N), 0.99 (s, br, 2H, NH2) ppm. Varying quantities of THF (with one molecule per formula unit the maximum) were observed in samples of 17. 13C{1H} NMR (101 MHz, THF-d8): δ 222.1 (m, COeq). 219.4 (app t, J = 8.8 Hz, COax), 168.0 (m, CN), 143.9 (m, ipso P(C6H5)2), 133.03 (s, ortho B(C6H5)2), 132.94 (s, ortho B(C6H5)2), 132.5 (app t, ortho P(C6H5)2), 126.2−126.3 (m, meta P(C6H5)2 and meta B(C6H5)2), 125.3 (s, para P(C6H5)2), 125.0 (s, para P(C6H5)2), 121.0 (s, para B(C6H5)2), 120.8 (s, para B(C6H5)2), 62.7 (m, (CH2CH2)2N), 47.3 (s, CH2NC), 41.7 (s, CH2NH2), 21.8 (s, (CH2CH2)2N) ppm. X-ray Crystallography. X-ray-quality crystals were obtained by diffusion of pentane into THF solutions (1−3), Et2O into THF solutions (10, 11, 16, 17), Et2O into CH3CN solutions (4−6, 8, 9, 15), and Et2O into a CH2Cl2 solution (14). Crystals were selected from the mother liquor in a N2-filled glovebag. Details regarding the data collection, structure solution, and refinement for each of these single-crystal X-ray studies are provided in the Supporting Information.

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ASSOCIATED CONTENT

S Supporting Information *

Text, figures, tables, and CIF files giving complete experimental details and characterization data, thermal ellipsoid drawings, details of crystallographic data collection, solution, and refinement, and crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. 1308

dx.doi.org/10.1021/om5001056 | Organometallics 2014, 33, 1300−1309

Organometallics

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Article

(19) Ueng, C.-H.; Shih, G.-Y. Acta Crystallogr., Sect. C 1992, C48, 988. (20) Aluri, B. R.; Peulecke, N.; Pietz, S.; Spannenberg, A.; Müller, B. H.; Schulz, S.; Drexler, H.-J.; Heller, D.; Al-Hazmi, M. H.; Mosa, F. M.; Wöhl, A.; Müller, W.; Rosenthal, U. Dalton Trans. 2010, 39, 7911. (21) Mrutu, A.; William, W. N.; Kemp, R. A. Inorg. Chem. Commun. 2012, 18, 110. (22) While the crystal data and structure refinement details of 8 (R1 = 0.0663, wR2 = 0.1365 (all data)) are sound, the SO2 ligand of 8 exhibits anomalously high displacements that could not be improved via disorder modeling. Consequently, only the metrical parameters of isostructural 9 are discussed herein. (23) Rousche, J.-C.; Dobson, G. R. Inorg. Chim. Acta 1978, 28, L139. (24) This apparent fac/mer isomerization that appears rapid in solution on the NMR time scale at ambient temperature has prompted VT NMR studies of 14, 15, and related M(CO)3(CNC6H4(2-NO2)) (L2) complexes containing bidentate phosphine ligands with varying electronic profiles. (25) (a) Schenk, W. A.; Urban, P. J. Organomet. Chem. 1991, 411, C27. (b) Schenk, W. A.; Urban, P.; Dombrowski, E. Chem. Ber. 1993, 126, 679. (26) The abbreviation chir or (S,S)-chiraphos is for (2S,3S)(−)-bis(diphenylphosphino)butane, a dppe analogue with methyl substituents on each carbon of the ligand backbone. (27) Schenk, W. A.; Baumann, F.-E. Chem. Ber. 1982, 115, 2615. (28) Schenk, W. A.; Karl, U.; Horn, M. R. Z. Naturforsch., B 1989, 44, 1513. (29) (a) Liu, C.-Y.; Chen, D.-Y.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T. Organometallics 1996, 15, 1055. (b) Kaufhold, O.; Stasch, A.; Edwards, P. G.; Hahn, F. E. Chem. Commun. 2007, 1822. (c) Kaufhold, O.; Flores-Figueroa, A.; Pape, T.; Hahn, F. E. Organometallics 2009, 28, 896. (d) Kaufhold, O.; Stasch, A.; Pape, T.; Hepp, A.; Edwards, P. G.; Newman, P. D.; Hahn, F. E. J. Am. Chem. Soc. 2009, 131, 306. (e) Flores-Figueroa, A.; Kaufhold, O.; Hepp, A.; Fröhlich, R.; Hahn, F. E. Organometallics 2009, 28, 6362. (f) Flores-Figueroa, A.; Pape, T.; Feldmann, K.-O.; Hahn, F. E. Chem. Commun. 2010, 46, 324. (30) (a) Flores-Figueroa, A.; Kaufhold, O.; Feldmann, K.-O.; Hahn, F. E. Dalton Trans. 2009, 9334. (b) Hahn, F. E.; Langenhahn, V.; Lügger, T.; Pape, T.; Le Van, D. Angew. Chem., Int. Ed. 2005, 44, 3759. (c) Basato, M.; Michelin, R. A.; Mozzon, M.; Sgarbossa, P.; Tassan, A. J. Organomet. Chem. 2005, 690, 5414. (31) Both 2-aminoethyl isocyanide and 2-aminophenyl isocyanide are similarly stabilized by the analogous W(CO)3(Ph2BP2) fragment on the basis of IR spectroscopy. However, protocols for obtaining analytically pure samples of [ASN][W(CO)3(CNCH2CH2NH2) (Ph2BP2)] and [ASN][W(CO)3(CNC6H4(2-NH2))(Ph2BP2)] have been elusive to date. Only the molybdenum complexes are discussed herein. (32) While pure isolated samples of each metal carbonyl intermediate in the synthesis of 17 could not be obtained, each complex was conveniently identified and monitored via IR spectroscopy of the reaction mixture, as detailed in the Experimental Section. (33) Hahn, F. E.; Tamm, M. Chem. Ber. 1992, 125, 119. Similar inconsistencies were noted previously upon comparison of these metrical parameters of 14 and 15 relative to those of M(CO)3(CNC6H4(2-NO2))(dppe) (M = Mo, W).

AUTHOR INFORMATION

Corresponding Author

*E-mail for P.J.F.: fi[email protected]. Present Addresses †

Department of Chemistry, Columbia University, MC3134, 3000 Broadway, New York, NY 10027, USA. ‡ Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, GA 30322, USA Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The National Science Foundation supported this research under Macalester College grants CHE-1011800 and DBI1039655. The latter award purchased a 400 MHz NMR spectrometer. P.J.F. thanks Victor G. Young, Jr. (University of Minnesota X-ray Crystallographic Laboratory), for his expertise and persistence. A new diffractometer with a Cu X-ray source in Dr. Young’s laboratory was purchased through a NSF grant (MRI-1224900) and funding from the University of Minnesota. P.J.F. is indebted to Rebecca C. Hoye and Robert C. Rossi for helpful discussions and to Macalester College endowed funds for two summer undergraduate research stipends (K.P.S. (2011), L.A. (2013)).

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