Synthesis and Reactivity of Ruthenium Hydride Complexes

Jan 15, 2014 - Ru complexes containing a tris(aminophosphine) ligand (N(NP)3) have been prepared and their reactivity examined. The complex ...
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Synthesis and Reactivity of Ruthenium Hydride Complexes Containing a Tripodal Aminophosphine Ligand Michael J. Sgro, Fatme Dahcheh, and Douglas W. Stephan* Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada S Supporting Information *

ABSTRACT: Ru complexes containing a tris(aminophosphine) ligand (N(NP)3) have been prepared and their reactivity examined. The complex [(N((CH2)2NHPiPr2)2(κ2N,P-((CH2)2NHPiPr2))RuCl][Cl] (1) is transformed to [(N((CH2)2NHPiPr2)2((CH2)2NPHiPr2))RuCl]Cl (2) on standing in solution. Deprotonation of the phosphonium center in 2 followed by anion exchange generates the Ru hydride complex [(N((CH 2 ) 2 NHPiPr 2 )((CH2)2NPiPr2)(CH2CHNHPiPr2))RuH][BPh4] (3), which can bind acetonitrile to give [(N((CH2)2NHPiPr2)2((CH2)2NPiPr2))Ru(CH3CN)][BPh4] (5). Protonation of 3 and 5 with either a 1 M solution of HCl in diethyl ether or NEt 3 HCl yields [(N((CH2)2NHPiPr2)2((CH2)2NPHiPr2))RuCl][BPh4] (6). Reaction of 3 with H2 gives the Ru hydride complex [(N((CH2)2NHPiPr2)2(κ2N,P((CH2)2NHPiPr2))RuH][BPh4] (8), which is deprotonated with KN(SiMe3)2 to give [(N((CH2)2NHPiPr2)2)((CH2)2NPiPr2)RuH] (9). This latter species reacts with H2 to generate [(N((CH2)2NHPiPr2)3)Ru(H)2] (10). The hydride species 3 is also shown to react with CO2, N2O, phenylacetylene, and 1-pentyne to give [(N((CH2)2NHPiPr2)2((CH2)2NP(CO2)iPr2))Ru][BPh4] (11), [(N((CH2)2NHPiPr2)2((CH2)2NP(O)iPr2))Ru][BPh4] (12), and [(N((CH2)2NHPiPr2)2((CH2)2NP(R)iPr2))Ru][BPh4] (R = C8H6 (13), C5H10 (14)), in which the substrate is bound to P and the metal center. In contrast, 9 does not react with N2O and alkyne but reacts with CO2 to give CO2 insertion into the N−P bond, yielding (N((CH2)2NHPiPr2)2((CH2)2N(CO2)PiPr2)RuH (15).

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INTRODUCTION

Scheme 1. CO2 Reduction by a Ru−Aminophosphine Complex

The cooperative activation of small molecules between metal centers and ligand fragments has received considerable attention over the years.1−8 Perhaps most notable is the cooperative activation of hydrogen exhibited by the Noyori hydrogenation catalysts,6,9−13 which have been further expanded in recent years.14−18 Milstein and co-workers have, more recently, exploited related cooperative actions of a ligand and metal center to uncover a reversible aromatization− dearomatization process,2 which can be utilized for water splitting,19 reversible NH activation,20 and the hydrogenation of carbonates, carbamates, and formates.21 We are interested in applying related cooperative strategies to the activation of small molecules. For example, while other researchers have developed metal-based systems to reduce CO2,22−30 we have recently been exploring the metal−ligand cooperativity of transition-metal complexes containing aminophosphine ligands31−33 with CO2. While hafnium complexes31 have been shown to effect the capture of CO2, a ruthenium species32 demonstrated the ability to catalyze the reduction of CO2 in the presence of HBpin to give pinBOMe and O(Bpin)2 (Scheme 1). In this full report we describe the synthesis and reactivity of related Ru tripodal aminophosphine complexes and examine the activation of H2, CO2, N2O, and terminal acetylenes. The impact on reactivity of neutral and cationic systems is also probed. © 2014 American Chemical Society

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RESULTS AND DISCUSSION Reaction of the tris(aminophosphine) ligand N(NP)3 with Ru(PPh3)3Cl2 over a 2.5 h period affords the yellow complex 1. The 1H and 31P{1H} NMR spectra are both quite broad, and little information could be obtained from either, but single crystals of 1 were obtained and the molecular structure was d et er m in ed t o be [ ( N( ( C H 2 ) 2 N H Pi Pr 2 ) 2 ( κ 2 N , P ((CH2)2NHPiPr2))RuCl][Cl] (Scheme 2, Figure 1). The distorted-octahedral geometry about the cationic ruthenium center in 1 is made up of a pseudo square plane of three phosphine donors and a N atom from the N(NP)3 ligand. The axial sites are occupied by the central nitrogen and a metalReceived: November 23, 2013 Published: January 15, 2014 578

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Scheme 2. Synthesis of 1−10

Figure 1. POV-Ray depiction of the molecular structure of the cation of 1: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms, except H2c, are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.687(2), N(2)−P(2) 1.732(2), N(3)−P(3) 1.679(2), P(1)−Ru 2.2907(5), P(2)−Ru 2.3494(5), P(3)−Ru 2.3288(5), N(2)−Ru 2.261(2), N(4)−Ru 2.182(2); N(2)−Ru−P(2) 44.09(4), N(4)−Ru−N(2) 81.42(6), N(4)−Ru−P(1) 90.86(4), N(2)−Ru−P(1) 156.75(5), N(4)−Ru−P(3) 89.33(4), N(2)−Ru− P(3) 99.59(5), P(1)−Ru−P(3) 102.23(2), N(4)−Ru−P(2) 93.16(4), N(2)−Ru−P(2) 44.09(4), P(1)−Ru−P(2) 115.25(2), P(3)−Ru− P(2) 142.37(2), N(4)−Ru−Cl(1) 177.07(5), N(2)−Ru−Cl(1) 99.14(5), P(1)−Ru−Cl(1) 89.68(2), P(3)−Ru−Cl(1) 87.74(2), P(2)−Ru−Cl(1) 89.21(2).

multiplicity integrating to 2:1. In a similar fashion, if the deprotonation reaction is followed by the addition of MeCN, 4 is obtained as a red solid in 85% yield (Scheme 2). The 31 1 P{ H} NMR spectrum of 4 also consists of two singlet resonances in a 2:1 ratio, one at 110.6 ppm and one at 69.7 ppm, with no evidence of P−H coupling. X-ray analysis of single crystals of 4 confirmed binding of N(NP)3 via two phosphorus atoms and a nitrogen atom of the NP fragments, in addition to the central N atom (Figure 2). The pseudo-trigonalbipyramidal geometry about Ru is completed by the coordination of acetonitrile, and thus 4 is formulated as [(N((CH 2 ) 2 NHPiPr2 ) 2 ((CH 2 ) 2 NPiPr2 ))Ru(CH 3 CN)][Cl]

bound chloride. The charge of the molecule is balanced by an outer-sphere chloride (Figure 1). Allowing a CD2Cl2 solution of 1 to stand for 24 h resulted in the complete conversion to the red product 2 (see the Supporting Information, Figures S1 and S2). We have previously reported that the reaction of N(NP)3 with Ru(PPh3)3Cl2 over a 24 h period affords complex 2, which was confirmed crystallographically to be the red species [(N((CH 2 ) 2 NHPiPr 2 ) 2 ((CH 2 ) 2 NPHiPr 2 ))RuCl][Cl].32 We have also previously reported that the reaction of 2 with KN(SiMe3)2 effects deprotonation of the phosphonium center and, following halide abstraction, generates the Ru hydride complex [(N((CH2)2NHPiPr2)((CH2)2NPiPr2)(CH2CHNHPiPr2))RuH][BPh4] (3).32 The hydride in 3 is generated from C−H activation of a methylene adjacent to the axial N atom, affording a coordinated iminium fragment as previously described. When the reaction of 2 and KN(SiMe3)2 was carried out in d8-THF, a single product was observed by 31 1 P{ H} NMR spectroscopy with two signals bearing no

Figure 2. POV-Ray depiction of the molecular structure of the cation of 4: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.678(2), N(2)−P(2) 1.670(2), N(3)−P(3) 1.711(2), P(1)−Ru 2.2408(5), P(2)−Ru 2.2876(6), N(3)−Ru 2.031(2), N(4)− Ru 2.143(2), N(5)−Ru 2.022(2); N(4)−Ru−N(5) 170.51(7). N(5)− Ru−N(3) 90.06(7), N(5)−Ru−N(4) 170.51(7), N(3)−Ru− N4 80.81(7), N(5)−Ru−P(1) 92.13(5), N(3)−Ru−P(1) 123.81(5), N(4)−Ru−P(1) 95.12(5), N(5)−Ru−P(2) 92.25(5), N(3)−Ru− P(2) 137.00(5), N(4)−Ru−P(2) 92.65(5), P(1)−Ru−P(2) 99.01(2). 579

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(2JHP = 25 Hz) in the 1H NMR spectrum attributable to a single H atom. A signal consistent with the presence of three NH groups is also observed, consistent with addition of H2. As the multiplicity of the hydride suggests that all three phosphines are bound to the metal center, these data reflect a formulation of 7 and 8 as [(N((CH2)2NHPiPr2)2(κ2N,P((CH2)2NHPiPr2))RuH][X] (X = Cl (7), BPh4 (8)). An X-ray diffraction study of single crystals of 7 confirmed the formulation (Figure 4).

(Figure 2). The Ru−P distances of 2.2408(5) and 2.2876(6) Å and Ru−N distances of 2.031(2) and 2.143(2) Å in 4 are shorter than those in 2. The bound acetonitrile gives rise to a Ru−N distance of 2.022(2) Å. Nonetheless, the N−P distances in 4 are similar to those in 2, with the exception of N−P, where the phosphine is pendant and the N is bound. This N−P distance of 1.7114(4) Å is elongated in comparison to the corresponding N−P bond in 2 (1.617(2) Å). This is consistent with the absence of the phosphonium proton. The analogous reaction of 3 with acetonitrile and Na[BPh4] in C6H5Br afforded the corresponding product [(N((CH2)2NHPiPr2)2((CH2)2NPiPr2))Ru(CH3CN)][BPh4] (5) in 88% yield. The formation of 5 from 3 requires reductive C− H elimination and coordination of acetonitrile (Scheme 2). The Ru−amido compounds 3 and 5 also react with either a 1 M solution of HCl in diethyl ether or NEt3HCl to give the new product 6, characterized by two signals in the 31P{1H} NMR spectrum at 117.4 and 41.3 ppm integrating in a 2:1 ratio. Compound 6 also shows a doublet of triplets at 7.22 ppm, in the 1H NMR spectrum, with a 1JHP value of 522 and a 3JHH value of 4 Hz. These data are consistent with the formulation of 6 as [(N((CH2)2NHPiPr2)2((CH2)2NPHiPr2))RuCl][BPh4] (Scheme 2). X-ray diffraction confirmed this formulation of 6 as the [BPh4] analogue of 2 (Figure 3). As was the case with 2,

Figure 4. POV-Ray depiction of the molecular structure of the cation of 7: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms, except for H(26) and H(3b), are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.681(2), N(2)−P(2) 1.683(2), N(3)−P(3) 1.727(2), P(1)−Ru 2.3126(6), P(2)−Ru 2.2635(6), P(3)−Ru 2.2566(6), N(3)−Ru 2.280(2), N(4)−Ru 2.296(2), H(26)−Ru 1.55(3); N(3)−Ru−P(3) 44.75(5), P(3)−Ru−P(2) 106.63(2), P(2)−Ru−N(3) 148.52(5), P(3)−Ru−N(4) 99.51(5), P(2)−Ru−N(4) 97.03(5), N(3)−Ru−N(4) 79.23(6), P(3)−Ru− P(1) 144.26(2), P(2)−Ru−P(1) 104.91(2), N(3)−Ru−P(1) 106.48(5), N(4)−Ru−P(1) 92.85(5), P(3)−Ru−H(26) 82.1(10), P(2)−Ru−H(26) 87(1), N(3)−Ru−H(26) 99(1), N(4)−Ru−H(26) 175(1), P(1)−Ru−H(26) 83(1).

The Ru center in 7 adopts a distorted-octahedral geometry with all three phosphines bound to Ru together with the central tertiary amine and a hydride. The remaining coordination site is filled by one of the amines adjacent to a phosphorus atom forming a tight three-membered N−Ru−P ring (44.71(4)°). The broadness of the NMR spectra of 7 and 8 suggest fluxional processes as has been seen in related N,P-bound aminophosphine complexes.34 Variable-temperature NMR experiments on 7 by both 31P{1H} and 1H NMR methods were performed over the temperature range 293−223 K (see the Supporting Information, Figures S3−S7). The 1H and 31 P{1 H} NMR spectra both begin to sharpen as the temperature is decreased to 223 K. Notably, in the 31P{1H} NMR spectra, coalescence points appear at 283 and 248 K. While the initial process likely arises from rapid exchange of the N−P binding modes, the latter process is thought to arise from inversion of the bound nitrogen. The amine of the bound N,P aminophosphine fragment in 7 is deprotonated with KN(SiMe 3 ) 2 , affording [(N((CH2)2NHPiPr2)2)((CH2)2NPiPr2)RuH] (9) as an amber solid in 87% yield (Scheme 2). The 1H NMR spectrum of 9 resembles that of 7 at low temperatures with a hydride pseudoquartet resonance (−18.48 ppm, 2JHP = 25 Hz) that is slightly upfield relative to the signal for 7. The 31P{1H} NMR spectrum shows three inequivalent phosphine environments and P−P coupling indicative of a trans phosphine disposition. X-ray

Figure 3. POV-Ray depiction of the molecular structure of the cation of 6: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms except H(1) omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.688(3), N(2)−P(2) 1.676(3), N(3)−P(3) 1.597(3), P(1)−Ru 2.2250(10), P(2)−Ru 2.2263(8), N(3)−Ru 2.101(3), N(4)−Ru 2.150(3); N(4)−Ru−Cl(1) 164.82(8). N(3)− Ru−N(4) 79,9(1), N(3)−Ru−P(1) 127.81(8), N(4)−Ru−P(1) 94.23(8), N(3)−Ru−P(2) 133.78(8), N(4)−Ru−P(2) 95.35(7), P(1)−Ru−P(2) 98.20(3), N(3)−Ru−Cl(1) 86.18(8), N(4)−Ru− Cl(1) 164.82(8), P(1)−Ru−Cl(1) 97.40(3), P(2)−Ru−Cl(1) 92.63(3).

the axial chloride is bent toward the phoshonium hydrogen atom with a N(4)−Ru−Cl(1) angle of 164.82(8)°, suggesting the presence of hydrogen bonding, a result supported by an H− Cl distance of 2.90(1) Å. The reaction of N(NP3) and Ru(PPh3)3HCl afforded the new complex 7 as a yellow solid in 91% yield. The analogous salt 8 was obtained from the reaction of 3 with 1 atm of H2 in 79% yield. Similarly, 7 was obtained via the reaction of 2 with LiBEt3H (Scheme 2). Complexes 7 and 8 exhibit almost identical NMR spectra, with the most diagnostic features being three broad signals in the 31P{1H} NMR spectrum. In the case of 8 these appear at 121.0, 104.2, and 59.0 ppm. There is also a pseudo-quartet (doublet of doublet of doublets) at −16.67 ppm 580

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diffraction studies revealed that 9 has a distorted-octahedral geometry with all three ligand phosphorus atoms coordinated as well as an amide adjacent to one of the phosphine donors forming the distorted square plane (Figure 5). The bound

Figure 6. POV-Ray depiction of the molecular structure of 10: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.694(5), N(2)−P(2) 1.702(5), N(3)−P(3) 1.695(6), P(1)−Ru 2.288(2), P(2)−Ru 2.313(2), P(3)−Ru 2.279(2), N(4)−Ru 2.337(5); P(1)−Ru−P(3) 144.94(6), P(3)−Ru−P(2) 107.48(6), P1−Ru−P(2) 104.45(6), P(3)−Ru−N(4) 96.6(1), P1−Ru−N(4) 95.5(1), P(2)−Ru−N(4) 93.5(1).

Figure 5. POV-Ray depiction of the molecular structure of 9: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms, except for H(25), are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.696(5), N(2)−P(2) 1.704(5), N(3)−P(3) 1.663(5), P(1)−Ru 2.279(2), P(2)−Ru 2.250(2), P(3)−Ru 2.269(1), N(3)−Ru 2.285(4), N(4)−Ru 2.317(4), H(25)−Ru 1.49(5); P(2)−Ru−P(3) 110.44(6), P(2)−Ru−P(1) 105.20(6), P(3)−Ru−P(1) 139.79(5), P(2)−Ru−N(3) 151.1(1), P(3)−Ru−N(3) 42.8(1), P(1)−Ru−N(3) 103.7(1), P(2)−Ru−N(4) 97.0(1), P(3)−Ru−N(4) 98.8(1). P(1)− Ru−N(4) 94.7(1), N(3)−Ru−N(4) 80.6(2), P(2)−Ru−H(25) 88(2). P(3)−Ru−H(25) 82(2), P(1)−Ru−H(25) 82(2), N(3)−Ru−H(25) 97(2), N(4)−Ru−H(25) 175(2).

Scheme 3. Synthesis of 11 and 12

amide provides a rare example of a pyramidal metal amide complex, one of the few crystallographically characterized.35,36 The tertiary amine donor and the hydride occupy the axial positions. While the N−Ru−P angle of 42.8(1)° in 9 suggests a considerable degree of strain in the system, compound 9 does not react with acetonitrile, in contrast to the related cation in 3. It does, however, react with H2 to give the white solid [(N((CH2)2NHPiPr2)3)Ru(H)2] (10) in 83% yield (Scheme 2). The 31P{1H} NMR spectrum displays two broadened singlets in a 2:1 ratio at 108.6 and 92.3 ppm, while the 1H NMR spectrum has two hydride signals at −10.4 and −21.0 ppm, both doublets of triplets of doublets. These data together with the molecular structure of 10 from X-ray crystallography are consistent with a distorted-octahedral coordination geometry in which a square plane is comprised of three phosphine donors and a hydride while the axial positions are occupied by the tertiary amine donor and a second hydride (Figure 6). In probing the reactivity of the hydride species 3, we have previously communicated that the reaction of 3 with CO2 gives [(N((CH 2 ) 2 NHPiPr 2 ) 2 ((CH 2 ) 2 NP(CO 2 )iPr 2 ))Ru][BPh 4 ] (11) as an orange solid (Scheme 3). The analogous reactivity of 3 with N2O prompted an immediate color change, affording the isolation of the deep orange product [(N((CH2)2NHPiPr2)2((CH2)2NP(O)iPr2))Ru][BPh4] (12) in 92% yield (Scheme 3, Figure 7). Elemental analysis of 12 suggested loss of N2, while 31P{1H} NMR data showed two singlets at 118.1 and 95.5 ppm and the 1H NMR spectrum showed no evidence of a hydride resonance. The molecular structure of 12 was determined, confirming the oxidation of a pendant phosphine, yielding a trigonal-bipyramidal geometry about Ru with an axially bound PO fragment, trans to the

central N donor, affording a four-membered N−P−O−Ru ring (Figure 7). Notably, the P(3)−N(3) bond is shorter than P−N single bonds, a situation similar to that observed in 2, 6, and 11. Compound 3 also reacts with phenylacetylene and 1pentyne, generating 13 and 14, respectively, in high yields (Scheme 4). The 31P{1H} NMR spectra of the compounds are similar, containing two slightly broadened signals in a 2:1 ratio. Though no coupling was observed in 14, the upfield signal at 99.9 ppm in the spectrum of 13 is a triplet with a P−P coupling constant of 5 Hz, supporting the equivalence of two of the phosphine donors. The complexes also share similar features in the 1H NMR spectra, as both lack a hydride and terminal alkyne resonances. However, a new doublet of triplets is observed in the 1H NMR spectrum of 14 at 5.94 ppm with H− P coupling of 67 Hz and H−H coupling of 7 Hz. X-ray diffraction studies of 13 and 14 confirmed the acetylene units undergo 1,2-proton migration and nucleophilic attack by the 581

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Figure 7. POV-Ray depiction of the molecular structure of the cation of 12: C; black, N; aquamarine, P; orange, O; red, Ru; scarlet. H atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.676(3), N(2)−P(2) 1.689(3), N(3)−P(3) 1.611(4), P(1)−Ru 2.250(1), P(2)−Ru 2.239(1), N(3)−Ru 2.006(3), N(4)−Ru 2.151(3), P(3)−O(1) 1.531(3); N(3)−Ru−O(1) 68.9(1), P(3)− O(1)−Ru 90.7(1), O(1)−P(3)−N(3) 101.4(2), N(3)−Ru−N(4) 79.8(1), N(3)−Ru−P(2) 129.6(1), N(4)−Ru−P(2) 97.73(9), N(3)−Ru−P(1) 133.6(1), N(4)−Ru−P(1) 96.33(9), P(2)−Ru− P(1) 96.87(4), N(4)−Ru−O(1) 148.7(1), N(2)−Ru−O(1) 102.57(7), P(1)−Ru−O(1) 104.49(7), N(3)−Ru−P(3) 35.3(1), N(4)−Ru−P(3) 115.07(9), P(2)−Ru−P(3) 119.13(4), P(1)−Ru− P(3) 126.05(3), O(1)−Ru−P(3) 33.72(7).

Figure 8. POV-Ray depiction of the molecular structure of the cation of 13: C, black; N, aquamarine; P, orange; O, red; H, purple; Ru, scarlet. H atoms, except H(26), are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.694(3), N(2)−P(2) 1.681(3), N(3)−P(3) 1.609(3), P(1)−Ru 2.2419(8), P(2)−Ru 2.2278(9), P(3)−Ru 2.8477(9), N(3)−Ru 2.009(3), N(4)−Ru 2.237(3), C(25)−Ru 2.090(4), P(3)−C(25) 1.832(4), C(25)− C(26) 1.303(6); N(3)−Ru−C(25) 73.0(1), P(3)−C(25)−Ru 92.9(2), P(3)−N(3)−Ru 103.3(2), N(3)−Ru−P(2) 129.9(1), C(25)−Ru−P(2) 104.9(1), N(3)−Ru−N(4) 77.8(1), C(25)−Ru− N(4) 150.7(1), P(2)−Ru−N(4) 95.42(8), N(3)−Ru−P(1) 132.3(1), C(25)−Ru−P(1) 100.7(1), P(2)−Ru−P(1) 98.56(3), N(4)−Ru− P(1) 96.85(8), N(3)−Ru−P(3) 33.36(9), C(25)−Ru−P(3) 40.0(1), P(2)−Ru−P(3) 128.02(3), N(4)−Ru−P(3) 110.69(8), P(1)−Ru− P(3) 120.67(3).

Scheme 4. Proposed Mechanism to 13 and 14

Ru phosphonium acetylide. Subsequent protonation of acetylide and nucleophilic attack of the transient vinylidene would afford the observed products (Scheme 4). Similar reaction pathways for amine and aryl attack of vinylidenes have been described by Caulton et al.37 and Jia et al.38 In this case, the energetically favored geometry results from nucleophilic attack by the pendant phosphine to generate the P−C bond, affording the vinyl products in which the P and aryl or alkyl substituent adopt a cis disposition. Recognizing the structural similarity of 3 and 9, reactions of 9 with CO2, N2O, and alkyne were studied. Surprisingly, in the last two cases, no reactions were observed even upon heating. However, in the case of CO2, exposure of the hydride complex 9 to 1 atm of CO2 gave the new product 15 in 80% yield. The 31 1 P{ H} NMR spectrum of 15 displays two doublets at 189.8 and 126.1 ppm (2JPP = 21 Hz) and a singlet at 67.0 ppm. The 1 H NMR spectrum is consistent with this inequivalence, showing 10 signals for the methylene linkers of the ligand backbone between 2.18 and 3.56 ppm in addition to 5 methine signals in the range from 1.39 to 2.08 ppm. A doublet of doublets at −26.15 ppm (2JHP = 50 Hz and 2JHP = 29 Hz) attributable to a Ru hydride is consistent with a vacant site trans to the hydride. The IR spectrum of 15 displays an absorption at 1657 cm−1. Use of 13CO2 in the preparation of 15-13C revealed a 13C{1H} NMR doublet at 164.3 ppm. The P−C coupling constant of 7 Hz is considerably smaller than that seen in 11, suggesting an alternative binding mode. A single-crystal X-ray diffraction study of 15 revealed that CO2 is inserted into the strained N−P bond in 9 (Scheme 5, Figure 10), yielding an overall square-pyramidal geometry about Ru in (N((CH2)2NHPiPr2)2((CH2)2N(CO2)PiPr2)RuH (15) with the

pendant phosphine, generating an alkene fragment bridging the P and Ru centers, and thus the products were formulated as [(N((CH2)2NHPiPr2)2((CH2)2NP(R)iPr2))Ru][BPh4] (R = C8H6 (13), C5H10 (14)) (Figures 8 and 9). In both fivecoordinate pseudo-trigonal-planar complexes, the trigonal plane is composed of two phosphines and an amide from the pendant phosphine group. The axial positions are occupied by the tertiary amine from N(NP3) as well as the carbon from the activated acetylene unit. The most notable feature of 13 and 14 is the strained four-membered NPCRu ring. Reactions of 3 with a mixture of d-phenylacetylene and 1pentyne gave a mixture of 13 and 14; deuterium was only incorporated into 13, suggesting an intramolecular process (Scheme 4). One possibility is that the coordination of alkyne to Ru prompts hydride migration to the ligand backbone carbon. Deprotonation of the alkyne would afford a transient 582

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Figure 10. POV-Ray depiction of the molecular structure of 15: C, black; N, aquamarine; P, orange; Ru, scarlet. H atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.693(4), N(2)−P(2) 1.675(4), P(1)−Ru 2.221(1), P(3)−Ru 2.195(1), N(3)−Ru 2.034(3), N(4)−Ru 2.223(3), C(25)−O(1) 1.383(5), C(25)−O(2) 1.222(5); N(3)−Ru−P(3) 79.8(1), N(3)− Ru−P(1) 152.5 (1), P(3)−Ru−P(1) 106.51(4), N(3)−Ru−N(4) 78.5(1), P(3)−Ru−N(4) 154.97(9), P(1)−Ru−N(4) 98.50(9).

Figure 9. POV-Ray depiction of the molecular structure of the cation of 14: C, black; N, aquamarine; P, orange; O, red; H, purple; Ru, scarlet. H atoms, except H(26), are omitted for clarity. Selected bond distances (Å) and angles (deg): N(1)−P(1) 1.686(5), N(2)−P(2) 1.678(4), N(3)−P(3) 1.604(5), P(1)−Ru 2.249(1), P(2)−Ru 2.223(1), P(3)−Ru 2.8367(14), N(3)−Ru 2.018(4), N(4)−Ru 2.237(4), C(25)−Ru 2.085(6), P(3)−C(25) 1.832(7), C(25)− C(26) 1.317(9); N(3)−Ru−C(25) 73.7(2), P(3)−C(25)−Ru 92.6(3), P(3)−N(3)−Ru 102.5(2). N(3)−Ru−P(2) 128.1(1), C(25)−Ru−P(2) 100.8(2), N(3)−Ru−N(4) 79.1(2), C(25)−Ru− N(4) 152.6(2), P(2)−Ru−N(4) 98.0(1), N(3)−Ru−P(1) 133.8(1), C(25)−Ru−P(1) 101.5(2), P(2)−Ru−P(1) 98.09(5), N(4)−Ru− P(1) 95.4(1), N(3)−Ru−P(3) 33.5(1), C(25)−Ru−P(3) 40.2(2), P(2)−Ru−P(3) 121.33(5), N(4)−Ru−P(3) 112.6(1), P(1)−Ru− P(3) 125.58(5).

ligand. The reactivity of the resulting hydride species 3 and 9 with CO2, N2O, and alkynes was examined. In the case of 3, where the metal is accessible as the hydride can migrate to the ligand backbone, the metal and pendant phosphine act in concert to capture these substrates, affording the binding of CO2 and alkyne between Ru and P. In the case of N2O, oxidation of the pendant phosphine affords a phosphine oxide coordinated to the Ru. In the case of 9, the metal is coordinatively saturated and thus this species acts as an amide nucleophile in reactions with CO2 with insertion of CO2 into the N−P bond. We are continuing to investigate the use of this ligand in designing new systems capable of small-molecule activation and catalysis.

Scheme 5. Synthesis of 15

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EXPERIMENTAL SECTION

General Considerations. All preparations were performed under an atmosphere of dry, O2-free N2 employing both Schlenk line techniques and inert atmosphere glove boxes. Solvents (THF, CH2Cl2, Et2O, hexane, and pentane) were purified employing a Grubbs type column system manufactured by Innovative Technology. C6H5Br was dried over CaH2 and distilled. Solvents were stored in the glovebox over 4 Å molecular sieves. 1H, 11B{1H} 13C{1H}, 19F{1H}, and 31 1 P{ H} NMR spectra were acquired on a Bruker Avance 400 MHz spectrometer. 1H and 13C NMR were internally referenced to deuterated CD2Cl2 (δ 5.32 ppm (1H), 53.84 ppm (13C)) and C6D5Br (δ 6.94 ppm (1H), 122.167 ppm (13C)) relative to Me4Si. NMR samples were prepared in the glovebox, capped, and sealed with Parafilm. 11B, 19F, and 31P resonances were referenced externally to BF3·Et2O, CFCl3, and 85% H3PO4, respectively. 1H−13C HSQC experiments were carried out using conventional pulse sequences to aid in the assignment of peaks in the 13C{1H} NMR spectroscopy. Coupling constants (J) are reported as absolute values. All glassware was dried overnight at 120 °C and evacuated for 1 h prior to use. Combustion analyses were performed in house employing a PerkinElmer 2400 Series II CHNS Analyzer. In some cases, repeated attempts to obtain satisfactory analyses were met with low carbon values. This appears to be the result of formation of Ru or B carbides during combustion. CD2Cl2 and C6D5Br were purchased from Cambridge Isotope Laboratories and were dried over CaH2, distilled, degassed, and stored under N2 in a glovebox. Ru(PPh3)3Cl2 and Ru(PPh3)3HCl were obtained from Strem Chemicals Inc. 13CO2 was

axial position being occupied by the hydride, although this could not be located in the X-ray solution. The formation of 15 stands in contrast to the formation of 11. The differing reaction pathway is most striking, given the structural similarity of 3 and 9. In the case of 3, migration of the hydride to the ligand backbone allows CO2 binding to the transiently coordinatively unsaturated Ru center, prompting nucleophilic attack by the pendant phosphine fragment. In contrast, for 9 the reaction is thought to be initiated by nucleophilic attack of CO2 by the amido N, prompting N−P bond cleavage. It is noteworthy that CO2 insertion into a Ru amide has been previously reported by Hartwig et al.39 and CO2 insertion into N−P bonds of main-group systems has also been described.40,41 However, the formation of 15 is to our knowledge the first to achieve such insertion into a N−P bond in a Ru coordination sphere.

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CONCLUSIONS In this paper we have described the synthesis of a number of ruthenium complexes containing the N(NP)3 aminophosphine 583

dx.doi.org/10.1021/om4011388 | Organometallics 2014, 33, 578−586

Organometallics

Article

(CH3)2CH), 21.90 (s, (CH3)2CH), 20.85 (s, (CH3)2CH), 20.64 (s, (CH3)2CH), 19.96 (bs, (CH3)2CH), 19.64 (bs, (CH3)2CH), 19.39 (d, 2 JCP 1 Hz, (CH3)2CH), 19.07 (s, (CH3)2CH; we did not observe CH3CN resonances. 31P{1H} NMR (CD3CN; δ, ppm): 110.53 (s, Ru−P bound PiPr2), 69.77 (s, Ru−N bound PiPr2). Anal. Calcd for C50H79N5P3RuB·0.5C6H5Br: C, 61.59; H, 7.95; N, 6.78. Found: C, 61.00; H, 7.79; N, 6.56. Synthesis of [(N((CH2)2NHPiPr2)2((CH2)2NPHiPr2))RuCl][BPh4] (6). [Et3NH][Cl] (16 mg, 0.116 mmol) was added to a solution of 5 in THF (94 mg, 0.098 mmol; 4 mL), and the reaction mixture was stirred for 12 h, at which point an orange solution was obtained. The solvent was removed in vacuo, and the orange residue was extracted into C6H6 and filtered over Celite, resulting in an orange solution. The solvent was then concentrated to 0.5 mL and layered with pentane. The product was isolated as orange needles after the solvent was removed in 96% yield (90 mg, 0.095 mmol). 1H NMR (CD2Cl2; δ, ppm): 7.36 (b, 8H, o-H BPh4), 7.22 (d of t, 1H, 1JHP 522 Hz, 2JHH 5 Hz, iPr2PH), 7.08 (t, 8H, 3JHH 7 Hz, m-H BPh4), 6.93 (t, 4H, 3JHH 7 Hz, p-H BPh4), 3.23 (m, 8H, CH2, NH), 2.97−2.80 (m, 4H, CH2), 2.60 (m, 6H, CH2, CH(CH3)2), 2.32 (m, 2H, CH(CH3)2), 1.45−1.12 (m, 36H, CH(CH3)2). 11B NMR (CD2Cl2; δ, ppm): −6.60 (s, BPh4). 13 C{1H} NMR (CD2Cl2; δ, ppm): 164.43 (q, 1JCB 49 Hz, ipso C BPh4), 136.34 (s, o-C BPh4), 126.02 (q, 3JCB 3 Hz, m-C BPh4), 122.17 (s, p-C BPh4), 65.58 (d, JCP 16 Hz, CH2), 61.92 (s, CH2), 45.52 (s, CH2), 40.56 (s, CH2), 34.37 (d of d, JCP 13 Hz, JCP 13 Hz, (CH3)2CH), 33.64 (t, JCP 15 Hz, (CH3)2CH), 24.78 (d, 1JCP 47 Hz, (CH3)2CH), 20.41 (s, (CH3)2CH), 19.60 (t, 2JCP 3, (CH3)2CH), 18.84 (s, (CH3)2CH), 18.75 (s, (CH3)2CH), 17.93 (d, 2JCP 2 Hz, (CH3)2CH), 17.29 (br s, (CH3)2CH). 31P{1H} NMR (CD2Cl2; δ, ppm): 117.35 (s, Ru−P bound PiPr2), 41.28 (s, Ru−N bound PiPr2). Anal. Calcd for C48H77N4P3RuClB: C, 60.66; H, 8.17; N, 5.90. Found: C, 60.81; H, 8.53; N, 6.05. Synthesis of [(N((CH2)2NHPiPr2)2(κ2N,P-(CH2)2NHPiPr2))RuH][Cl] (7). A solution of N(NP)3 in CH2Cl2 (161 mg, 0.325 mmol; 4 mL) was added to a purple suspension of Ru(PPh3)3HCl in CH2Cl2 (300 mg, 0.313 mmol; 2 mL), giving no immediate change. The reaction mixture was stirred for 12 h, at which point a clear orange solution was obtained. The solvent was removed in vacuo, and the yellow-orange solid was washed with diethyl ether (3 × 5 mL). The yellow solid was then dissolved in a minimal amount of CH2Cl2 layered with pentane. The product was isolated as orange-yellow crystals after the solvent was removed in 91% yield (187 mg, 0.296 mmol). 1H NMR (CD2Cl2; δ, ppm): 3.24 (b, 6H, CH2), 2.64 (b, 6H, CH2), 2.02 (b, 6H, CH(CH3)2), 1.23 (b, 36H, CH(CH3)2), −16.79 (bquart, 1H, 2JHP 26 Hz, Ru−H). 13C{1H} NMR (CD2Cl2; δ, ppm): 64.39 (b, CH2), 43.00 (b, CH2), 30.86 (b, (CH3)2CH), 19.07 (b, (CH3)2CH). 31P{1H} NMR (CD2Cl2; δ, ppm): 122.61 (br), 104.29 (br), 55.55 (br). Anal. Calcd for C24H58N4P3RuCl·CH2Cl2: C, 41.85; H, 8.44; N, 7.81. Found: C, 42.00; H, 8.22; N, 7.68. Synthesis of [(N((CH2)2NHPiPr2)2(κ2N,P-(CH2)2NHPiPr2))RuH][BPh4] (8). A red solution of 3 in C6H5Br (75 mg, 0.082 mmol; 2 mL) was transferred to a tube bomb and sealed. The solution was degassed using three freeze−pump−thaw cycles before being warmed to room temperature and charged with 1 atm of hydrogen. The mixture was stirred at room temperature for 24 h, yielding a pale orange solution. The volatiles were removed in vacuo, and a yellow solid was obtained. The solid was washed with pentane and dried. The yellow product was obtained in 79% yield (59 mg, 0.065 mmol). 1H NMR (CD2Cl2; δ, ppm): 7.34 (b, 8H, o-H BPh4), 7.04 (t, 8H, 3JHH 7 Hz, m-H BPh4), 6.90 (t, 4H, 3JHH 7 Hz, p-H BPh4), 3.09 (bm, 6H, CH2), 2.50 (bm, 6H, CH2), 2.04 (b, 6H, CH(CH3)2), 1.86 (bm, 3H, NH), 1.19 (b, 36H, CH(CH3)2), −16.67 (bquart, 1H, 2JHP 25 Hz, Ru−H). 11B NMR (CD2Cl2; δ, ppm): −6.58 (s, BPh4). 13C{1H} NMR (CD2Cl2; δ, ppm): 164.42 (q, 1JCB 49 Hz, ipso C BPh4), 136.36 (bs, o-C BPh4), 126.08 (m, 3 JCB 3 Hz, m-C BPh4), 122.25 (s, p-C BPh4), 64.15 (b, CH2), 42.86 (b, CH2), 31.22 (b, (CH3)2CH), 18.84 (b, (CH3)2CH). 31P{1H} NMR (CD2Cl2; δ, ppm): 120.95 (br), 104.16 (br), 58.96 (br). Anal. Calcd for C48H78N4P3RuB: C, 62.91; H, 8.59; N, 6.12. Found: C, 63.35; H, 8.71; N, 6.07.

obtained from Aldrich Chemical Co. N((CH2)2NPiPr2)3(N(NP)3) was prepared as previously described.32 Synthesis of [(N((CH2)2NHPiPr2)2(κ2N,P-(CH2)2NHPiPr2))RuCl][Cl] (1). A solution of N(NP)3 in CH2Cl2 (150 mg, 0.303 mmol; 4 mL) was added to a suspension of Ru(PPh3)3Cl2 in CH2Cl2 (193 mg, 0.201 mmol; 4 mL), giving a green-blue solution. After the mixture was stirred for 2.5 h, a green-yellow solution was obtained. The solvent was concentrated to 1 mL, and 15 mL of pentane was added to precipitate a yellow solid which was isolated in 63% yield (63 mg, 0.127 mmol). Yellow blocks suitable for X-ray diffraction were obtained by layering a solution of Ru(PPh3)3Cl2 (26 mg, 0.0271 mmol) in 0.5 mL of CH2Cl2 with a solution of N((CH2)2NHPiPr2)3 (15 mg, 0.0303 mmol) in 1 mL of hexane in an NMR tube. 1H NMR (CD2Cl2; δ, ppm): 3.50−2.01 (br m, 21H, NH, CH2 (CH3)2CH), 1.23 (br m, 36H, (CH3)2CH). 13C NMR (CD2Cl2; δ, ppm): 43.04 (br m, CH2), 32.32 (br m, (CH3)2CH), 20.46 (br m, (CH3)2CH), 19.15 (br m, (CH3)2CH). 31P{1H} NMR (CD2Cl2; δ, ppm): 80.14 (bs, Ru−P bound PiPr2). Anal. Calcd for C24H57Cl2N4P3Ru: C, 43.24; H, 8.62; N, 8.40. Found: C, 42.32; H, 8.22; N, 8.16. Synthesis of [(N((CH2)2NHPiPr2)2((CH2)2NPiPr2))Ru(CH3CN)][Cl] (4). A solution of K(N(SiMe3)2 and THF (30 mg, 0.150 mmol; 2 mL) was added dropwise to a red suspension of 2 in THF (100 mg, 0.150 mmol; 4 mL), giving a slightly cloudy red solution after 5 min. The reaction mixture was stirred for 12 h, at which point it was dried. The solid was extracted with C6H6 and filtered through Celite to give a clear deep red solution. Neat acetonitrile was added (250 μL), causing the solution to lighten slightly. The reaction mixture was stirred overnight to give a cloudy pink-red mixture. The solution was concentrated under vacuum, and pentane was added to precipitate the red product. The supernatant was decanted off, and the fluffy red powder was dried. The solid was then dissolved in acetonitrile and layered with diethyl ether, giving the product as red blocks in 85% yield (85 mg, 0.128 mmol). 1H NMR (CD3CN; δ, ppm): 3.32 (m, 4H, CH2), 3.20 (bs, 2H, NH), 3.07 (m, 2H, CH2), 2.78 (m, 2H, NH), 2.65 (m, 2H, CH2), 2.59 (m, 2H, CH2), 2.46 (m, 2H, 3JHH 7 Hz, CH(CH3)2), 2.27 (s, 3H, CH3CN), 2.08 (m, 4H, 3JHH 7 Hz, CH(CH3)2), 1.35 (m, 12H, 3JHH 7 Hz, CH(CH3)2), 1.20 (m, 12H, 3 JHH 7 Hz, CH(CH3)2), 1.07 (m, 12H, 3JHH 7 Hz, CH(CH3)2). 13 C{1H} NMR (CD3CN; δ, ppm): 126.85 (s, CH3CN), 65.52 (d, JCP 4 Hz, CH2), 62.54 (s, CH2), 49.72 (bd, JCP 10 Hz, CH2), 40.73 (s, CH2), 34.92 (m, JCP 12 Hz, (CH3)2CH), 34.68 (m, JCP 12 Hz, (CH3)2CH), 26.84 (d, JCP 25 Hz, (CH3)2CH), 22.07 (s, (CH3)2CH), 21.90 (s, (CH3)2CH), 20.85 (s, (CH3)2CH), 20.64 (s, (CH3)2CH), 19.96 (s, (CH3)2CH), 19.75 (t, 2JCP 1 Hz, (CH3)2CH), 19.47 (d, 2JCP 1 Hz, (CH3)2CH), 19.18 (s, (CH3)2CH), 6.66 (s, CH3CN). 31P{1H} NMR (CD3CN; δ, ppm): 110.56 (s, Ru−P bound PiPr2), 69.72 (s, Ru−N bound PiPr2). Crystals were crushed and placed under vacuum prior to elemental analysis. Anal. Calcd for C26H59N5P3RuCl: C, 46.50; H, 8.86; N, 10.44. Found: C, 46.29; H, 8.96; N, 10.05. Synthesis of [(N((CH2)2NHPiPr2)2((CH2)2NPiPr2))Ru(CH3CN)][BPh4] (5). A red solution of 3 in C6H5Br (75 mg, 0.082 mmol; 2 mL) was prepared in a 4 dram vial equipped with a stir bar. Neat acetonitrile was added (250 μL), giving an immediate color change from orange to red. The reaction mixture was stirred overnight to give a clear red solution before being layered with pentane. The supernatant was decanted off of the red solid, which was then dried. The product was obtained in 88% yield (69 mg, 0.072 mmol). 1H NMR (CD3CN; δ, ppm): 7.28 (b, 8H, o-H BPh4), 7.00 (t, 8H, 3JHH 7 Hz, m-H BPh4), 6.85 (t, 4H, 3JHH 7 Hz, p-H BPh4), 3.28 (m, 4H, CH2), 3.07 (m, 2H, CH2), 2.73 (m, 4H, NH, CH2), 2.63 (m, 2H, CH2), 2.57 (m, 2H, CH2), 2.43 (m, 2H, 3JHH 7 Hz, CH(CH3)2), 2.25 (s, 3H, CH3CN), 2.08 (m, 4H, 3JHH 7 Hz, CH(CH3)2), 1.38 (m, 6H, 3 JHH 7 Hz, CH(CH3)2), 1.31 (m, 6H, 3JHH 7 Hz, CH(CH3)2), 1.20 (m, 12H, 3JHH 7 Hz, CH(CH3)2), 1.08 (m, 12H, 3JHH 7 Hz, CH(CH3)2). 11 B NMR (CD3CN; δ, ppm): −6.53 (s, BPh4). 13C{1H} NMR (CD3CN; δ, ppm): 164.87 (q, 1JCB 50 Hz, ipso C BPh4), 136.81 (q, 2 JCB 1 Hz, o-C BPh4), 126.66 (q, 3JCB 3 Hz, m-C BPh4), 122.83 (s, p-C BPh4), 65.47 (d, JCP 4 Hz, CH2), 62.50 (s, CH2), 49.77 (bd, JCP 10 Hz, CH2), 40.72 (s, CH2), 34.94 (m, JCP 12 Hz, (CH3)2CH), 34.62 (m, JCP 12 Hz, (CH3)2CH), 26.84 (d, JCP 25 Hz, (CH3)2CH), 22.07 (s, 584

dx.doi.org/10.1021/om4011388 | Organometallics 2014, 33, 578−586

Organometallics

Article

Synthesis of (N((CH2)2NHPiPr2)2(κ2N,P-(CH2)2NHPiPr2))RuH (9). To a stirred yellow suspension of 7 in THF (150 mg, 0.237 mmol; 4 mL) was added a clear colorless solution of K(N(SiMe3)2 and THF (47 mg, 0.237 mmol; 2 mL) dropwise over 5 min, giving a cloudy amber mixture. The reaction mixture was stirred overnight before being dried. The solid was extracted with diethyl ether and filtered through a plug of Celite to give a clear amber solution. The solvent was removed in vacuo, yielding a brown-yellow solid. Pentane was added and the suspension stored at −35 °C. The solvent was removed and the solid dried. Further batches of solid were obtained from the supernatant by repeating the previous procedure. The product was obtained as a yellow solid in 87% yield (124 mg, 0.209 mmol). 1H NMR (C6D5Br; δ, ppm): 3.42 (bs, 1H, NH), 3.25 (m, 1H, CH2), 3.00 (m, 2H, CH2), 2.76 (m, 4H, CH2), 2.52 (m, 1H, CH2), 2.29 (m, 2H, 3JHH 8 Hz, CH(CH3)2), 2.16 (m, 2H, CH2), 1.98 (m, 2H, CH2), 1.85 (m, 3H, CH(CH3)2 and NH), 1.68 (m, 2H, CH(CH3)2), 1.28 (m, 30H, CH(CH3)2), 0.99 (m, 6H, 3JHH 8 Hz, CH(CH3)2), −18.48 (pseudo-quart, 1H, 2JHP 25 Hz, RuH) . 13C{1H} NMR (C6D5Br; δ, ppm): 64.92 (bm, CH2), 50.08 (bm, CH2), 42.06 (bm, CH2), 35.38 (bm, CH2), 31.48 (bm, (CH3)2CH), 29.99 (bm, (CH3)2CH), 28.19 (bm, (CH3)2CH), 26.13 (bm, (CH3)2CH), 22.73 (bs, (CH3)2CH), 20.19 (bs, (CH3)2CH), 19.83 (bs, (CH3)2CH), 19.49 (bs, (CH3)2CH), 19.21 (bs, (CH3)2CH), 17.68 (bs, (CH3)2CH), 17.36 (bs, (CH3)2CH), 16.80 (bs, (CH3)2CH). 31P{1H} NMR (C6D5Br; δ, ppm): 124.58 (bs, Ru−P bound PiPr2), 109.20 (bd, 2JPP 241 Hz, Ru− P bound PiPr2), 40.76 (bd, 2JPP 241 Hz, Ru−N−P metallacycle PiPr2). Anal. Calcd for C24H57N4P3Ru: C, 48.37; H, 9.65; N, 9.41; Found C, 48.79; H, 9.51; N, 9.55. Synthesis of (N((CH2)2NHPiPr2)3)RuH2 (10). A solution of 9 in THF (75 mg, 0.126 mmol; 4 mL) was transferred to a tube bomb and sealed. The yellow solution was frozen in liquid nitrogen and the head space evacuated under vacuum. The mixture was warmed to room temperature, and hydrogen was added before the vessel was sealed. The mixture was stirred at room temperature for 24 h, yielding a very pale yellow solution. The volatiles were removed in vacuo, and a pale yellow solid was obtained. The solid was washed with pentane and dried. The white product was obtained in 83% yield (63 mg, 0.105 mmol). 1H NMR (C6D5Br; δ, ppm): 3.14 (m, 4H, CH2), 3.01 (m, 2H, CH2), 2.26 (m, 4H, CH2), 2.03 (m, 4H, 2H 3JHH 7 Hz, CH(CH3)2, 2H CH2), 1.90 (m, 4H, 3JHH 7 Hz, CH(CH3)2), 1.79 (m, 2H, NH), 1.49 (m, 1H, NH), 1.27 (m, 18H, 3JHH 7 Hz, CH(CH3)2), 1.18 (m, 12H, 3 JHH 7 Hz, CH(CH3)2), 1.04 (m, 6H, 3JHH 7 Hz, CH(CH3)2), −10.43 (d of t of d, 1H, 2JHH 7 Hz, 2JHP 73 Hz, 2JHP 31 Hz, Ru−H equatorial), −21.04 (d of t of d, 1H, 2JHH 7 Hz, 2JHP 27 Hz, 2JHP 20 Hz, Ru−H axial). 13C{1H} NMR (C6D5Br; δ, ppm): 69.46 (t, JCP 3 Hz, CH2), 63.85 (d, JCP 7 Hz, CH2), 41.76 (t, JCP 6 Hz, CH2), 41.52 (t, JCP 13 Hz, CH2), 35.48 (s, (CH3)2CH), 31.88 (s, (CH3)2CH), 19.90 (s, (CH3)2CH), 19.82 (s, (CH3)2CH), 18.89 (s, (CH3)2CH), 18.53 (t, 2 JCP 4 Hz, (CH3)2CH), 17.87 (s, (CH3)2CH), 17.76 (s, (CH3)2CH). 31 1 P{ H} NMR (C6D5Br; δ, ppm): 108.61 (br, 2P), 92.27 (br, 1P). Anal. Calcd for C24H59N4P3Ru: C, 48.20; H, 9.95; N, 9.38; Found C, 48.48; H, 9.73; N, 9.52. Synthesis of [(N((CH2)2NHPiPr2)2((CH2)2NP(O)iPr2))Ru][BPh4] (12). An orange-yellow solution of 3 (75 mg, 0.082 mmol) in C6H5Br (2 mL) was transferred to a 25 mL bomb and degassed using three freeze−pump−thaw cycles. The bomb was filled with 1 atm of N2O, and the contents were stirred for 12 h, giving an orange suspension. Pentane was added to the mixture to complete precipitation of an orange solid. The solvent was decanted, and the remaining solid was dissolved in 2 mL of C6H5Br and layered with pentane. The product was isolated as an orange solid after the solvent was removed in 92% yield (70 mg, 0.075 mmol). 1H NMR (C6D5Br; δ, ppm): 7.82 (b, 8H, o-H BPh4), 7.21 (t, 8H, 3JHH 7 Hz, m-H BPh4), 7.07 (t, 4H, 3JHH 7 Hz, p-H BPh4), 2.97 (m, 2H, CH2), 2.68 (m, 4H, CH2, CH(CH3)2), 2.49 (m, 2H, CH2), 1.94 (m, 4H, CH2), 1.83 (m, 8H, 3JHH 7 Hz, CH(CH3)2, CH2, NH), 1.15 (m, 12H, 3JHH 7 Hz, CH(CH3)2), 0.96 (m, 24H, 3JHH 7 Hz, CH(CH3)2). 11B NMR (C6D5Br; δ, ppm): −6.04 (s, BPh4). 13C{1H} NMR (C6D5Br; δ, ppm): 164.39 (q, 1JCB 49 Hz, ipso C BPh4), 136.59 (q, 2JCB 2 Hz, o-C BPh4), 125.72 (q, 3JCB 3 Hz, mC BPh4), 121.92 (s, p-C BPh4), 67.99 (m, CH2), 61.81 (s, CH2), 45.92

(m, JCP 1 Hz, CH2), 39.70 (s, CH2), 32.57 (m, (CH3)2CH), 30.52 (m, JCP 21 Hz, (CH3)2CH), 29.86 (m, (CH3)2CH), 18.91 (s, (CH3)2CH), 18.66 (s, (CH3)2CH), 18.42 (s, (CH3)2CH), 18.27 (s, (CH3)2CH), 16.48 (d, 2JCP 3 Hz, (CH3)2CH), 16.22 (s, (CH3)2CH). 31P{1H} NMR (C6D5Br; δ, ppm): 118.12 (s, Ru−P bound PiPr2), 85.50 (s, O PiPr2). Crystals were crushed and placed under vacuum prior to elemental analysis. Anal. Calcd for C48H76N4P3RuOB: C, 61.99; H, 8.24; N, 6.02. Found: C, 61.03; H, 8.36; N, 5.90. Synthesis of [(N((CH2)2NHPiPr2)2((CH2)2NP(C8H6)iPr2))Ru][BPh4] (13) and [(N((CH2)2NHPiPr2)2((CH2)2NP(C5H10)iPr2))Ru][BPh4] (14). These products were obtained in a similar manner, and thus only one preparation is detailed. For 13, an orange-yellow solution of 3 (80 mg, 0.088 mmol) in C6H5Br (2 mL) was prepared in a 4 dram vial equipped with a stir bar and neat phenylacetylene was added (100 uL, 0.880 mmol). The solution immediately changed color from orange to red. The reaction mixture was stirred for 12 h, at which point it was layered with pentane. The product was isolated as dark red needles after the solvent was removed in 94% yield (84 mg, 0.083 mmol). Data for 13 are as follows. 1H NMR (CD2Cl2; δ, ppm): 7.34 (m, 9H, 1H PCCH, 8H o-H BPh4), 7.27 (m, 4H, Ar-H C6H5), 7.05 (t, 8H, 3 JHH 7 Hz, m-H BPh4), 6.98 (d, 1H, 3JHH 7 Hz, Ar-H C6H5), 6.90 (t, 4H, 3JHH 7 Hz, p-H BPh4), 3.34 (m, 2H, 3JHH 7 Hz, CH2), 3.17 (m, 4H, 3JHH 7 Hz, CH2), 3.01 (m, 2H, 3JHH 7 Hz, JHP 4.0 Hz, CH(CH3)2), 2.77 (m, 2H, 3JHH 7 Hz, CH2), 2.61 (m, 4H, 3JHH 7 Hz, CH2), 2.37 (m, 2H, NH), 2.23 (m, 2H, 3JHH 7 Hz, CH(CH3)2), 2.08 (m, 2H, 3JHH 7 Hz, CH(CH3)2), 1.35 (m, 21H, 3JHH 7 Hz, CH(CH3)2), 1.19 (m, 9H, 3 JHH 7 Hz, JHP 15.3 Hz, CH(CH3)2), 1.06 (m, 6H, 3JHH 7 Hz, JHP 15 Hz, CH(CH3)2. 11B NMR (CD2Cl2; δ, ppm): −6.53 (s, BPh4). 13 C{1H} NMR (CD2Cl2; δ, ppm): 164.45 (q, 1JCB 50 Hz, ipso C BPh4), 152.61 (d, 2JCP 10 Hz, PCCH), 143.04 (d, 3JCP 15 Hz, Cipso C6H5), 136.35 (q, 3JCB 1 Hz, o-C BPh4), 127.67 (s, Ar-C C6H5), 127.40 (s, ArC C6H5), 126.70 (d, JCP 2 Hz, Ar-C C6H5), 126.02 (q, 3JCB 3 Hz, m-C BPh4), 122.16 (s, p-C BPh4), 64.98 (d, JCP 11 Hz, CH2), 63.02 (s, CH2), 46.90 (d, JCP 4 Hz, CH2), 40.87 (s, CH2), 37.12 (t, JCP 12 Hz, (CH3)2CH), 34.43 (t, JCP 21 Hz, (CH3)2CH), 34.33 (d, JCP 24 Hz, (CH3)2CH), 32.31 (d, JCP 26 Hz, (CH3)2CH), 20.45 (s, (CH3)2CH), 20.15 (s, (CH3)2CH), 19.39 (s, (CH3)2CH), 18.66 (s, (CH3)2CH), 17.76 (d, 2JCP 1, (CH3)2CH), 17.06 (d, 2JCP 3, (CH3)2CH). 31P{1H} NMR (CD2Cl2; δ, ppm): 117.58 (bs, Ru−P bound PiPr2), 99.89 (t, 3 JPP 5 Hz, C−PiPr2). Anal. Calcd for C56H82N4P3RuB·1/2C6H5Br: C, 64.71; H, 7.78; N, 5.12. Found: C, 64.68; H, 7.68; N, 4.77. Data for 14 are as follows: dark red needles in 95% yield (95 mg, 0.083 mmol) from 3 (80 mg, 0.088 mmol) and 1-pentyne (90 uL, 0.880 mmol). 1H NMR (C6D5Br; δ, ppm): 7.84 (bs, 8H, o-H BPh4), 7.23 (t, 8H, 3JHH 7 Hz, m-H BPh4), 7.08 (t, 4H, 3JHH 7 Hz, p-H BPh4), 5.94 (d of t, 1H, 3JHH 7 Hz, 3JHP 67 Hz, PCCH), 2.76 (m, 4H, CH2), 2.64 (m, 2H, CH2), 2.56 (m, 2H, 3JHH 7 Hz, CH(CH3)2), 2.19 (m, 2H, CH2), 2.02 (m, 4H, CH2), 1.87 (m, 2H, NH, 2H, 3JHH 7 Hz, CH(CH3)2), 1.74 (m, 2H, 3JHH 7 Hz, CH(CH3)2, 2H, 3JHH 7 Hz, CH2pentyne), 1.22 (t, 2H, 3JHH 7 Hz, CH2-pentyne), 1.01 (m, 36H, 3JHH 7 Hz, CH(CH3)2), 0.82 (m, 3H, 3JHH 7 Hz, CH3-pentyne). 11B NMR (C6D5Br; δ, ppm): −6.00 (s, BPh4). 13C{1H} NMR (C6D5Br; δ, ppm): 164.46 (q, 1JCB 49 Hz, ipso C BPh4), 153.01 (d, 2JCP 12 Hz, PCCH), 136.62 (q, 3JCB 1 Hz, o-C BPh4), 125.71 (q, 3JCB 3 Hz, m-C BPh4), 121.88 (s, p-C BPh4), 63.94 (d, JCP 13 Hz, CH2), 61.68 (s, CH2), 45.60 (d, JCP 4 Hz, CH2), 42.28 (d, 3JCP 18 Hz, C3 C5H8), 39.95 (s, CH2), 35.82 (m, JCP 26 Hz, (CH3)2CH), 33.90 (m, JCP 27 Hz, (CH3)2CH), 33.58 (m, JCP 13 Hz, (CH3)2CH), 30.45 (d, JCP 26 Hz, (CH3)2CH), 22.76 (d, 4JCP 2 Hz, C4 C5H8), 19.98 (s, (CH3)2CH), 19.58 (s, (CH3)2CH), 18.57 (s, (CH3)2CH), 18.25 (s, (CH3)2CH), 17.17 (s, (CH3)2CH), 17.03 (d, 2JCP 3, (CH3)2CH), 13.81 (s, C5 C5H8). 31 1 P{ H} NMR (C6D5Br; δ, ppm): 118.28 (bs, Ru−P bound PiPr2), 92.64 (s, C-PiPr2). Crystals were crushed and placed under vacuum prior to elemental analysis. Anal. Calcd for C53H84N4P3RuB: C, 64.82; H, 8.62; N, 5.71. Found: C, 63.63; H, 8.25; N, 5.56. Synthesis of (N((CH2)2NHPiPr2)2((CH2)2N(CO2)PiPr2)RuH (15). A solution of 9 in C6H5Br (85 mg, 0.143 mmol; 4 mL) was prepared in a 25 mL Schlenk bomb and degassed using three freeze−pump− thaw cycles. The bomb was charged with 1 atm of CO2, and the 585

dx.doi.org/10.1021/om4011388 | Organometallics 2014, 33, 578−586

Organometallics

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contents were stirred for 6 h, giving a clear deep red solution. The reaction mixture was transferred to a 4 dram vial, and the product was precipitated with pentane as a red solid. The product was washed with pentane before being redissolved in C6H5Br and layered with pentane for recrystallization. The product was obtained as red crystals in 80% yield (80 mg, 0.114 mmol). 1H NMR (C6D5Br; δ, ppm): 3.56 (m, 1H, CH2), 3.36 (m, 1H, CH2), 3.16 (m, 1H, CH2), 2.91 (m, 4H, CH2), 2.71 (m, 1H, CH2), 2.51 (m, 1H, CH2), 2.38 (m, 1H, CH2), 2.29 (m, 1H, CH2), 2.18 (m, 1H, CH2), 2.08 (m, 1H, 3JHH 7 Hz, CH(CH3)2), 1.87 (m, 1H, 3JHH 7 Hz, CH(CH3)2), 1.76 (m, 1H, 3JHH 7 Hz, CH(CH3)2), 1.58 (m, 1H, 3JHH 7 Hz, CH(CH3)2), 1.39 (m, 3H, 3JHH 7 Hz, CH(CH3)2, NH), 1.30 (m, 6H, CH(CH3)2), 1.16 (m, 10H, 3JHH 7 Hz, CH(CH3)2, NH), 1.06 (m, 6H, 3JHH 7 Hz, CH(CH3)2), 0.96 (m, 12H, 3JHH 7 Hz, CH(CH3)2), 0.67 (m, 3H, 3JHH 7 Hz, CH(CH3)2), −26.15 (d of d, 1H, 2JHP 50 Hz, 2JHP 29 Hz, Ru−H). 13C{1H} NMR (C6D5Br; δ, ppm): 164.28 (d, 2JCP 7 Hz, CO2), 63.21 (bs, CH2), 60.99 (s, CH2), 57.72 (bs, CH2), 44.57 (s, CH2), 43.85 (s, CH2), 42.33 (bs, CH2), 31.96 (m, JCP 21 Hz, (CH3)2CH), 31.65 (m, JCP 13 Hz, (CH3)2CH), 31.33 (m, 1JCP 20 Hz, (CH3)2CH), 30.93 (m, (CH3)2CH), 27.71 (m, 1JCP 16 Hz, (CH3)2CH), 26.61 (m, 1JCP 14 Hz, (CH3)2CH), 19.85 (b, (CH3)2CH), 19.49 (b, (CH3)2CH), 19.40 (b, (CH3)2CH), 19.18 (b, (CH3)2CH), 19.05 (s, (CH3)2CH), 18.97 (s, (CH3)2CH), 18.75 (b, (CH3)2CH), 18.30 (s, (CH3)2CH), 18.14 (b, (CH3)2CH), 18.02 (s, (CH3)2CH), 17.72 (b, (CH3)2CH), 17.53 (s, (CH3)2CH), 17.29 (b, (CH3)2CH), 16.81 (b, (CH3)2CH), 16.35 (b, (CH3)2CH). 31P{1H} NMR (C6D5Br; δ, ppm): 189.75 (d, 2JPP 21 Hz, O−P), 126.06 (d, 2JPP 21 Hz, Ru−P), 67.04 (s, pendant P). IR: 1657.07 cm−1. Anal. Calcd for C25H57N4P3RuO2: C, 46.92; H, 8.98; N, 8.76. Found: C, 46.74; H, 8.71; N, 8.68. X-ray Data Collection, Reduction, Solution, and Refinement. Single crystals were coated in Paratone-N oil in the glovebox, mounted on a MiTegen Micromount, and placed under an N2 stream. The data were collected on a Bruker Apex II diffractometer. The data were collected at 150(±2) or 223(±2) K for all crystals. Data reduction was performed using the SAINT software package and an absorption correction applied using SADABS. The structures were solved by direct methods using XS and refined by full-matrix least squares on F2 using XL as implemented in the SHELXTL suite of programs.42 All non-hydrogen atoms were refined anisotropically. Carbon-bound hydrogen atoms were placed in calculated positions using an appropriate riding model and coupled isotropic temperature factors.

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ASSOCIATED CONTENT

S Supporting Information *

Figures giving NMR spectra and CIF files and tables giving crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for D.W.S.: [email protected]. Funding

NSERC of Canada Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support was received from the NSERC of Canada; D.W.S. is grateful for the award of a Canada Research Chair. REFERENCES

(1) Grützmacher, H. Angew. Chem., Int. Ed. 2008, 47, 1814. (2) Gunanathan, C.; Milstein, D. Acc. Chem. Res. 2011, 44, 588. (3) Annibale, V. T.; Song, D. RSC Adv. 2013, 3, 11432. (4) van der Vlugt, J. I.; Reek, J. N. H. Angew. Chem., Int. Ed. 2009, 48, 8832. 586

dx.doi.org/10.1021/om4011388 | Organometallics 2014, 33, 578−586