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Base-Promoted Transmetalation Reactions of Protic N‑Heterocyclic Carbenes and Acyclic Diamino Carbenes from MnI to AuI: A Mechanistic Study Javier Ruiz,*,† Daniel Sol,† Juan F. Van der Maelen,*,‡ and Marilín Vivanco† †

Departamento de Química Orgánica e Inorgánica and ‡Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, E-33006 Oviedo, Spain S Supporting Information *

ABSTRACT: DFT theoretical calculations for the base-induced transmetalation process of protic N-heterocyclic carbenes of imidazol-2-ylidene type from Mn(I) to Au(I) have been carried out. The reaction mechanism found involves the formation of key reaction intermediates bearing a pure bridging imidazolyl ligand between manganese and gold, as well as transition states showing η2 coordination of this ligand, first to gold and then to manganese, before the transmetalation process is completed. In addition, similar DFT calculations have been performed on protic acyclic diamino carbene complexes, showing analogous transferring of the carbene moiety from Mn(I) to Au(I) to afford remarkable mangana-N-heterocyclic carbenes of gold.

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tautomer is the basis of this behavior.11 A singular reaction pathway for the transmetalation of pNHCs from Mn(I) to Au(I) has been developed by our group. pNHC complexes of Mn(I) were obtained either by tautomerization of imidazoles12,13 or by coupling of coordinated isocyanide and propargylamine.14 An acid/base protocol allows for the transferring of pNHC from Mn(I) to Au(I) through isolable imidazolate heterometallic intermediates (Scheme 1),12,15 showing the preference of the carbene carbon atom for the softer Au(I) ion.

INTRODUCTION Since the discovery of the Ag2O method for the synthesis of Nheterocyclic carbene (NHC) complexes of AgI from the corresponding imidazolium salts by Lin and co-workers,1 the use of these complexes as carbene transfer agents has been widely applied for the preparation of a great diversity of transition-metal NHC complexes by transmetalation.2 To a much lesser extent, other metal NHC derivatives have also been used in transmetalation reactions, such as those of W(0),3 Cr(0),3b Cu(I),4 Au(I),3c Ni(II),5 Zr(IV),6 and Zn(II).7 The mechanism of this process remains rather elusive, but recent studies on ligand exchange in NHC silver(I) complexes suggest an associative mechanism,8 which is also consistent with the existence of several dimetallic complexes bearing NHCs as bridging ligands.9 Among NHC complexes, those containing one or two N−H functionalities within the imidazole cycle (so-called protic NHCs or pNHCs) have been little studied, though they have gained increasing interest in recent years because they offer additional reactivity patterns such as easy postfunctionalization, formation of hydrogen bonds for supramolecular assembly, and substrate recognition in cooperative catalysis.10 Naturally, the Ag2O method is not applicable to the generation of protic NHCs, as the N−H function is easier to deprotonate than the C−H function in protic imidazolium salts, which hinders the use of transmetalation protocols for the synthesis of protic NHC transition-metal complexes. In fact, as far as we know, no direct reaction transfer of a protic NHC between metal atoms has been described in the literature so far. The enhanced stability of the imidazole heterocycle with respect to its NHC © XXXX American Chemical Society

Scheme 1. Complete Transmetalation Reaction of a Protic NHC from MnI to AuI

In parallel reactions, a translocation process of the carbene carbon atom from Mn(I) to Au(I) also took place in acyclic protic diaminocarbene (ADC) complexes (Scheme 2), allowing the formation of unique metalla-N-heterocyclic carbenes.16,17 To gain knowledge about the transmetalation process of protic NHCs and ADCs, which could be useful for designing future Received: January 5, 2017

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DOI: 10.1021/acs.organomet.7b00009 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

intermediate when using 1-methylbenzimidazol-2-ylidene as the NHC ligand.15b From 2 to its isomer 3, calculations suggest that the reaction path follows the sequence 2−TS1−I1−TS2− I2−TS3−3. The graphic representation of the energetic profile for the mechanism may be seen in Figure 1, while theoretically optimized geometries for all molecules involved are depicted in Figure 2, and selected bond distances and angles are collected in Tables 1 and 2, respectively.

Scheme 2. Transmetalation Reaction of a Protic ADC from MnI to AuI Affording a Metallacyclic Carbene

applications of this reaction approach which remains essentially unexplored in the literature, we have now carried out DFT mechanistic calculations which suggest the formation of key reaction intermediates and transition states bearing a bridging imidazolyl carbon atom between manganese and gold and support the preferential coordination of the carbene moiety to gold in the heterometallic intermediates, thus justifying the observed transmetalation process.

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RESULTS AND DISCUSSION Transmetalation of Protic NHCs. The overall transmetalation process is summarized in Scheme 3. Experimentally, Scheme 3. Proposed Mechanism for the NHC Transfer from Mn(I) to Au(I)

Figure 1. Theoretical reaction pathway for the isomerization of 2 to 3 (free energies are given in kcal mol−1).

As can be deduced from Figure 1, compound 3 is considerably more stable than compound 2, thus justifying the observed isomerization process (calculated free energy variation from 2 to 3 −11.198 kcal mol−1). The change of coordination of the carbene carbon atom from manganese in 2 to gold in 3 goes through the intermediate complex I1, where the imidazolyl carbon atom adopts a bridging bonding mode between both metal atoms. As mentioned in the Introduction, several examples of complexes containing NHCs as pure bridging ligands through the carbon atom have been reported in the literature, though they all show a symmetric interaction with two equal metallic atoms.9 In complex I1 the Au1−C2 distance (2.068 Å) is considerably shorter than the Mn1−C2 distance (2.455 Å), which reflects the stronger tendency of the Au(I) ion to bind the imidazolyl carbon atom with respect to the Mn(I) ion. Interestingly, the reaction path passes through the first transition state TS1, which contains the azolyl ligand η2 coordinated to gold, with the Au atom bonded to both N3 and C2 atoms with similar bond distances, thus initiating the interaction of the carbon atom C2 with gold, with parallel weakening of the Au1−N3 and Mn1−C2 bonds, as can be seen in the significant increase of the Au1−N3 bond distance (from 2.045 Å in 2 to 2.396 Å in TS1) and in the moderate enlargement of the Mn1−C2 bond length (from 2.069 Å in 2 to 2.116 Å in TS1). A further increase in the latter distance is observed when passing from the transition state TS1 to the intermediate I1 (from 2.116 Å in TS1 to 2.455 Å in I1), while the Au1−C2 bond distance in I1 is shortened from 2.295 to 2.068 Å. A substantial closing of both Mn1−C2−

we have observed that the Mn(I)-NHC complex A reacts with [AuCl(PPh3)] in the presence of KOH to afford the heterometallic complex 3, which on treatment with HClO4 affords the Au(I)-NHC complex 4, in such a way that 3 can be considered as an isolable intermediate in the acid/base promoted transmetalation process of the NHC from Mn(I) to Au(I). It must be pointed out that the treatment of complex A with [AuCl(PPh3)] in the absence of KOH does not afford complex 4; therefore, the presence of a deprotonating agent is mandatory for the transmetalation reaction to take place. The first step appears to be the formation of the imidazolyl derivative 1, which was detected by IR spectroscopy in the first moments of the reaction course and has been isolated and fully characterized in an independent experiment (see the Supporting Information).18 We assume that then coordination of the [AuPPh3]+ fragment occurs to afford 2. Compound 2 has not been observed even when performing the reaction at low temperature, but we have detected spectroscopically a similar B


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Organometallics

Mn1−(CO)eq axes is parallel to the C2−Au1−P1 line in intermediate I1, while in complex I2 it is exactly the other Mn1−(CO)eq axis that is parallel to the same line. This rotation passes through the transition state TS2, where the C2−Au1− P1 line is parallel to the bisection of both Mn1−(CO)eq axes. As can be seen in Table 1, bond distances for I1 and I2 are essentially the same, with only small differences in bond angles. Therefore, it is not surprising that both intermediates have very similar Gibbs energies (Figure 1), with the transition state TS2 less than 2 kcal mol−1 above them. Finally, from the intermediate I2, where the Mn atom is bonded to the C2 atom of the imidazolyl ligand, to the product 3, where the Mn atom is bonded to the N3 atom of the same ligand, the reaction path passes through a third transition state (TS3), for which the imidazolyl ligand is η2 coordinated to the Mn atom with rather long Mn1−C2 (2.662 Å) and Mn1−N3 (2.773 Å) bond lengths. An additional decrease in the Au1−C2 bond distance (from 2.070 Å in I2 to 2.043 Å in TS3) is also observed. It is noteworthy that the segments N3−Au1−P1 and C2−Au1−P1 are closer to linear in both cationic complexes 2 and 3 (176.48 and 176.04°, respectively) than in any other compound on this path. This feature, together with the many other structural analogies between these compounds, shown in Tables 1 and 2, accounts for their much lower Gibbs energies (Figure 1). In all the structures of the calculated reaction intermediates and transition states found in the transformation from 2 to 3, that is I1, I2, TS1, TS2, and TS3, a closing of the N(C)−Au−PPh3 bond angle is observed together with an approximation of the imidazole plane to the equatorial plane of the manganese complex. This structural motif could explain the slowing of the above transformation when a more steric congested protic NHC ligand such as 1-methylbenzimidazol-2-ylidene is used, which allows the spectroscopic detection of a complex of type 2, before translocation of the Mn(I) and Au(I) metal ions occurs.15b In view of this, we argued that perhaps an increase in the steric hindrance of the substituents at phosphorus or at the carbon backbone of the imidazole cycle could help to stabilize complexes of type 2. With this in mind, we checked the reaction of compound A with [AuCl(P(2,4,6-trimethoxyphenyl)3)] and KOH. Though the cone angle of tris(2,4,6trimethoxyphenyl)phosphine (188°)19 is considerably higher than that of triphenylphosphine (145°).20 the result of the reaction was once again formation of a compound of type 3 without observation of any intermediate species type 2 (see the Supporting Information). We also carried out reactions of similar Mn(I) complexes containing either 1-methyl-5-phenylimidazol-2-ylidene or 1-methyl-4,5-diphenylimidazol-2-ylidene ligand with [AuCl(PPh3)], giving a similar result: that is, the immediate formation of complexes of type 3 (see Supporting Information). It can be concluded that the transmetalation

Figure 2. Theoretically optimized geometries for all molecules involved in the transformation of 2 to 3. Hydrogen atoms omitted for clarity. Color code: Au, yellow; Mn, magenta; P, orange; O, red; N, blue; C, gray.

N1 and Mn1−C2−N3 bond angles is also seen on going from 2 to I1, while at the same time the Mn atom keeps its octahedral coordination. It is worth noting the very small value of the angles N3−C2−Au1 (76.68°) and C2−N3−Au1 (68.78°) in TS1 in comparison to those in I1 and 2 (116.61 and 132.41°, respectively), which results from the η 2 coordination of the imidazolyl ligand to gold. Structural changes between intermediate complexes I1 and I2 are less dramatic, since they involve just a rotation of the [Mn]⊕ group about the (CO)ax−Mn1−C2 axis in such a way that one of the

Table 1. Selected Bond Distances (Å) from the Theoretically Optimized Geometries for All Species Involved in the Transformation of 2 to 3

2 TS1 I1 TS2 I2 TS3 3

Mn1−C2

C2−N1

C2−N3

2.069 2.116 2.455 2.380 2.433 2.662

1.400 1.420 1.422 1.430 1.424 1.414 1.393

1.376 1.396 1.363 1.369 1.367 1.366 1.363

Mn1−N3

2.773 2.051 C

C2−Au1 2.295 2.068 2.092 2.070 2.043 2.036

N3−Au1

Au1−P1

2.045 2.396

2.361 2.362 2.405 2.395 2.403 2.409 2.420


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Organometallics Table 2. Selected Bond Angles (deg) from the Theoretically Optimized Geometries for All Species Involved in the Transformation of 2 to 3 2 TS1 I1 TS2 I2 TS3 3

Mn1−C2−N1

Mn1−C2−N3

129.71 127.26 117.68 120.34 122.60 120.43

125.96 118.86 107.73 108.53 101.07 80.00

N3−C2−Au1 76.68 116.61 111.07 113.75 118.90 132.28

C2−N3−Au1 132.41 68.78

C2−Au1−P1 167.38 168.20 170.06 168.62 174.38 176.04

N3−Au1−P1 176.48 157.08

process of the carbene moiety from Mn(I) to Au(I) is extremely favorable for a variety of imidazole and phosphine ligands, which precludes isolation of the intermediate complexes of type 2. Transmetalation of Protic ADCs. A result closely related to that described above is observed in the reaction of the protic ADC complex B with [AuCl(PPh3)] in basic media, showing the transfer of the carbene carbon atom from manganese to gold. In this case the carbene moiety remains anchored to the manganese complex through both nitrogen atoms, which bond to two electrophilic centers thereof: the Mn(I) ion and the carbon atom of an equatorial carbonyl ligand.16 This process is summarized in Scheme 4. As a first step a deprotonation Scheme 4. Proposed Mechanism for the ADC Transfer from Mn(I) to Au(I) Figure 3. Theoretical reaction pathway for the transformation of 7 to 8 (free energies are given in kcal mol−1).

C3 atom, the reaction path passes through a transition state (TS4), in which the Au atom is bonded to both N2 and C3 atoms with similar bond distances, although with a significant increase in the Au1−N2 bond distance (from 2.031 Å in 7 to 2.378 Å in TS4) as well as in the Mn1−C3 bond distance (from 2.130 Å in 7 to 2.291 Å in TS4). This is a clear indication of the significant weakening of the Mn1−C3 and Au1−N2 bonds in transition state TS4, which anticipates subsequent translocation of the metal ions. At the same time, the Mn atom is close enough to the N2 atom in TS4 (3.083 Å) to favor the transition to intermediate I3, where a real Mn1−N2 bond is formed (2.055 Å) simultaneously with the breaking of both Mn1−C3 and Au1−N2 bonds (see Figure 4). Note the close similarity of TS4 with the transition state TS1 involved in the transmetalation process of protic NHCs described before, both of them featuring very similar structural parameters in the η2 coordination mode to gold, showing that both mechanisms are closely related. Structural changes between intermediate complexes I3 and I4 are less dramatic, although they involve half of a full rotation of the phenyl group attached to the N4 atom about the C3−N4 axis (N2−C3−N4−C(Ph) and Au1− C3−N4−C(Ph) torsion angles in I3: 39.84 and −148.79°, respectively, versus −162.75 and 17.02°, respectively, in I4). As can be seen in Table 3, the Mn1−N2 bond distance is slightly shorter in I4 than in I3 while the opposite is true for the Au1− C3 bond distance, with only small differences in bond angles of both intermediates. However small, these changes account for the significant stabilization of complex I4 relative to complex I3 (Figure 3), with the transition state TS5 being less than 1 kcal mol −1 above the latter compound. Finally, from the intermediate I4, where no bonding exists between N4 and

reaction of compound B takes place, giving neutral complex 5, which is stable enough to be isolated.21 5 is unable to react with [AuCl(PPh3)], unless KOH is present in the reaction media; therefore we assume the intermediate formation of the anionic complex 6 before metalation of the NMe group with the [Au(PPh3)]+ fragment occurs to yield neutral complex 7. From 7 to the final complex 8, our calculations suggest that the reaction path is given by the sequence 7−TS4−I3−TS5−I4− TS6−8. The graphic representation of the mechanism may be seen in Figure 3, while theoretically optimized geometries for all molecules involved are depicted in Figure 4, and selected bond distances and angles are collected in Tables 3 and 4, respectively. Conversion of complex 7 to complex 8 takes place through the two intermediate complexes I3 and I4. From complex 7, where the Au atom of the AuPPh3 moiety is bonded to the N2 atom, to intermediate I3, where the Au atom is bonded to the D


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C5 bond distance (from 1.789 Å in I4 to 1.812 Å in TS6) and the C3−N4 bond distance (from 1.329 Å in I4 to 1.336 Å in TS6), together with a slight opening of the N2−C3−N4 bond angle (118.78° in I4 and 120.32° in TS6). As in the mechanism described before for the transmetalation process of protic NHCs, it is also noteworthy in the present mechanism that the angles N2−Au1−P1 and C3−Au1−P1 are closer to linear in both complexes 7 and 8 (175.32 and 176.52°, respectively) than in any other compound in this path. This feature, together with the many other structural parameters described above and shown in Tables 3 and 4, accounts for their much lower Gibbs energies (Figure 3).

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CONCLUSION We have carried out herein DFT theoretical calculations for the base-induced transmetalation process of protic N-heterocyclic carbenes of imidazol-2-ylidene type from Mn(I) to Au(I), which support a reaction mechanism involving the formation of key reaction intermediates bearing a pure bridging imidazolyl ligand between manganese and gold, as well as transition states showing η2 coordination of this ligand, first to gold and then to manganese, before the transmetalation process is completed. In addition, similar DFT calculations have been performed on protic acyclic diamino carbene complexes, showing analogous transferring of the carbene moiety from Mn(I) to Au(I) to afford remarkable mangana-N-heterocyclic carbenes of gold. Considering that transmetalation reactions of protic Nheterocyclic carbenes and acyclic diamino carbenes are practically unknown in the literature, the result described herein could pave the way for designing transmetalation processes of these protic carbene ligands by controlling the hard/soft character of the metals involved, as well as the nature of the ancillary ligands present in the complexes thereof.

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Figure 4. Theoretically optimized geometries for all molecules involved in the transformation of 7 to 8. Hydrogen atoms are omitted for clarity. Color code: Au, yellow; Mn, magenta; P, orange; O, red; N, blue; C, gray.

Table 3. Selected Bond Distances (Å) from the Theoretically Optimized Geometries for All Species Involved in the Transformation of 7 to 8 7 TS4 I3 TS5 I4 TS6 8

Mn1−C3

C3−N4

2.130 2.291

1.320 1.323 1.326 1.329 1.329 1.336 1.388

Mn1−N2

2.055 2.058 2.036 2.059 2.035

C3−Au1 2.327 2.045 2.046 2.066 2.079 2.053

N2−Au1

Au1−P1

2.031 2.378

2.364 2.388 2.436 2.438 2.450 2.448 2.420

THEORETICAL CALCULATIONS

Density functional theory (DFT) computations have been performed with the GAUSSIAN09 program package,22 starting from our experimental geometry for cation 3 and complex 8 obtained from Xray single-crystal diffraction data12,16 and using the B3LYP, B3PW91, and B3P86 Becke three-parameter exchange functional with the nonlocal Lee−Yang−Parr, Perdew−Wang, and Perdew correlation functionals, respectively, and the Vosko−Wilk−Nusair local correlation functional,23 in order to check the accuracy of the three methods in our calculations. The all-electron 6-31G(d) and 6-311++G(3df,3pd) basis sets were employed for C, H, N, O, P, and Mn atoms at different steps of the procedure (the former basis set for the geometry optimization processes and the latter for the single-point electronic structure calculations at the optimized geometries), while the LanL2DZ effective core potential and the large all-electron WTBS basis set (“Well-Tempered Basis Set” of Huzinaga and co-workers)24 were used for the Au atom (again, the former in the geometry optimization and the latter in electronic structure calculations). The usual Berny algorithm with the quasi-Newton RFO method and Pulay’s Direct Inversion procedure for SCF cycles were used for most of the optimizations made, although in some cases (the saddle points of reaction paths) the slower but more reliable quadratically convergent SCF procedure and the Newton−Raphson optimization algorithm were utilized instead.25 Frequency analysis was performed at every stationary point found, within the B3P86/6-31G(d,p)/LanL2DZ level of theory, characterizing compounds 2, I1, I2, and 3 as minima in the mechanism summarized in Scheme 3, as well as compounds 7, I3, I4, and 8 as minima in the mechanism shown in Scheme 4. Subsequently, using these minima as starting points at the same level of theory, three transition states (having one imaginary frequency each one of them) were found in both mechanisms: TS1, TS2, and TS3 in the first mechanism and TS4, TS5, and TS6 in the second mechanism.

C5 (belonging to an equatorial carbonyl ligand) atoms, to the product 8, where both atoms are bonded together, thus closing the five-membered ring Mn1−N2−C3−N4−C5 forming the corresponding carbamoyl group, the reaction path passes through a third transition state (TS6) arising from I4 by rotation around the C3−N2 bond, in such a way that the N4 and C5 atoms become placed close to each other although still not bonded (2.701 Å), with a small increase in both the Mn1− E


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Organometallics Table 4. Selected Bond Angles (deg) from the Theoretically Optimized Geometries for All Species Involved in the Transformation of 7 to 8 N4−C3−Au1 7 TS4 I3 TS5 I4 TS6 8

133.11 109.94 112.71 119.29 115.29 118.73

C3−N2−Au1

75.37 123.32 124.77 121.94 122.46 126.21

156.69 172.25 171.16 174.36 160.86 176.52

N2−Au1−P1 175.32 137.96

Principado de Asturias (Projects FC-15-GRUPIN14-011 and GRUP-IN14-060). D.S. thanks the Principado de Asturias for a scholarship.

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REFERENCES

(1) Wang, H. M. J.; Lin, I. J. B Organometallics 1998, 17, 972−975. (2) (a) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251, 642− 670. (b) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 105, 3978− 4008. (3) (a) Liu, S. T.; Hsieh, T. Y.; Lee, G. H.; Peng, S. M. Organometallics 1998, 17, 993−995. (b) Ku, R. Z.; Hung, J. C.; Cho, J. Y.; Kiang, F. M.; Reddy, K. R.; Chen, Y. C.; Lee, K. J.; Lee, J. H.; Lee, G. H.; Peng, S. M.; Liu, S. T. Organometallics 1999, 18, 2145− 2154. (c) Liu, S. T.; Lee, C. I.; Fu, C. F.; Chen, C. H.; Liu, Y. H.; Elsevier, C. J.; Peng, S. M.; Chen, J. T. Organometallics 2009, 28, 6957−6962. (4) (a) Furst, M. R. I.; Cazin, C. S. J. Chem. Commun. 2010, 46, 6924−6925. (b) Venkatachalam, G.; Heckenroth, M.; Neels, A.; Albrecht, M. Helv. Chim. Acta 2009, 92, 1034−1045. (5) (a) Liu, B.; Liu, X.; Chen, C.; Chen, C.; Chen, W. Organometallics 2012, 31, 282−288. (b) O, W. W. N.; Lough, A. J.; Morris, R. H. Organometallics 2009, 28, 6755−6761. (c) O, W. W. N.; Lough, A. J.; Morris, R. H. Organometallics 2011, 30, 1236−1252. (6) Zhang, X.; Wright, A. M.; DeJonker, N. J.; Hollis, T. K.; Hammer, N. I.; Webster, C. E.; Valente, E. J. Organometallics 2012, 31, 1664− 1672. (7) Armstrong, D. R.; Baillie, S. E.; Blair, V. L.; Chabloz, N. G.; Diez, J.; Garcia-Alvarez, J.; Kennedy, A. R.; Roberston, S. D.; Hevia, E. Chem. Sci. 2013, 4, 4259−4266. (8) Su, H.; Pérez, L. M.; Lee, S.; Reibenspies, J. H.; Bazzi, H. S.; Bergbreiter, D. E. Organometallics 2012, 31, 4063−4071. (9) (a) Han, X.; Koh, L.; Liu, Z.; Weng, Z.; Hor, T. S. A. Organometallics 2010, 29, 2403−2405. (b) Gischig, S.; Togni, A. Organometallics 2005, 24, 203−205. (c) Liu, X.; Chen, W. Organometallics 2012, 31, 6614−6622. (d) Catalano, V. J.; Munro, L. B.; Strasser, C. E.; Samin, A. F. Inorg. Chem. 2011, 50, 8465−8476. (e) Chen, C.; Qiu, H.; Chen, W. J. Organomet. Chem. 2012, 696, 4166−4172. (10) For a review, see: Jahnke, M. C.; Hahn, F. E. Coord. Chem. Rev. 2015, 293−294, 95−115. (11) McGibbon, G. A.; Heinemann, C.; Lavorato, D. J.; Schwarz, H. Angew. Chem., Int. Ed. Engl. 1997, 36, 1478−1481. (12) Ruiz, J.; Perandones, B. F. J. Am. Chem. Soc. 2007, 129, 9298− 9299. (13) A similar tautomerization process applied to rhenium and molybdenum complexes was later reported by Pérez and co-workers: (a) Huertos, M. A.; Pérez, J.; Riera, L.; Menéndez-Velázquez, A. J. Am. Chem. Soc. 2008, 130, 13530−13531. (b) Huertos, M. A.; Pérez, J.; Riera, L.; Díaz, J.; López, R. Angew. Chem., Int. Ed. 2010, 49, 6409− 6412. (c) Brill, M.; Díaz, J.; Huertos, M. A.; López, R.; Pérez, J.; Riera, L. Chem. - Eur. J. 2011, 17, 8584−8595. (14) (a) Ruiz, J.; García, G.; Mosquera, M. E. G.; Perandones, B. F.; Gonzalo, M. P.; Vivanco, M. J. Am. Chem. Soc. 2005, 127, 8584−85. (b) Ruiz, J.; Perandones, B. F.; García, G.; Mosquera, M. E. G. Organometallics 2007, 26, 5687−5695.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00009. Additionally, checkpoint files for each compound (those of geometry optimization procedures, frequency and thermodynamic properties calculations, and electronic energy calculations) are available from the authors upon request. Experimental details for the synthesis and characterization of the new compounds, coordinates for the theoretically optimized structures of compounds 2, 3, 7, 8, I1−I4, and TS1−TS6, and large graphic representations of theoretical structures, including atomic labels and hydrogen atoms (PDF) Cartesian coordinates for all calculated structures (XYZ)

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C3−Au1−P1

127.81 71.27

Additionally, application of the IRC method showed that each transition state effectively connects with their corresponding minima.26 Every ground state wave function obtained for all of the compounds was analyzed and found to be stable. Scaled zero-point energies (ZPE) were added to the final electronic energies in order to obtain reliable enthalpies and free energies at room temperature (scale factor used for ZPE: 0.9804).27 Absolute energies obtained for each compound were rather different by using different calculation levels, as expected,28 although relative energies between different compounds were basically constant, with differences no larger than 0.1 kcal mol−1 by exchanging either method or basis set. B3P86/6-311++G(3df,3pd)/WTBS(Au) was the final model adopted for further discussion. Bearing in mind that the use of relativistic Hamiltonians has been shown to be essential in many instances in order to obtain accurate quantitative results from calculations on compounds containing thirdrow transition-metal atoms,29 we tried to further optimize all previous structures by using the scalar relativistic ZORA Hamiltonian, the PW91 density functional, among others, and the all-electron relativistic QZ4P basis set for all atoms (as well as core potentials), as implemented in the ADF2012 program package, 30 although unfortunately full convergence was only achieved for compounds 3 and 8.

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N2−C3−Au1

AUTHOR INFORMATION

Corresponding Authors

*E-mail for J.F.V.d.M.: [email protected]. *E-mail for J.R.: [email protected]. ORCID

Javier Ruiz: 0000-0002-4496-9185 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Spanish Ministerio de Economı ́a y Competitividad (Projects MINECO-FEDER MAT2013-40950-R and CTQ2015-66959-P) and by the F


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