Relativistic Four-Component DFT Calculations of 1H NMR Chemical

ARTICLE pubs.acs.org/JPCA

Relativistic Four-Component DFT Calculations of 1H NMR Chemical Shifts in Transition-Metal Hydride Complexes: Unusual High-Field Shifts Beyond the Buckingham
Stephens Model Peter Hrob
arik,*,†,‡ Veronika Hrob
arikov
a,†,§ Florian Meier,† Michal Repisk
y ,‡,|| Stanislav Komorovsk
y ,‡ and Martin Kaupp*,† †

Institut f€ur Chemie, Technische Universit€at Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany Institute of Inorganic Chemistry, Slovak Academy of Sciences, D
ubravsk
a cesta 9, SK-84536 Bratislava, Slovakia § Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynsk
a dolina, SK-84215 Bratislava, Slovakia Center for Theoretical and Computational Chemistry, Department of Chemistry, University of Trømso, N-9037, Trømso, Norway

)

‡

bS Supporting Information ABSTRACT: State-of-the-art relativistic four-component DFT-GIAObased calculations of 1H NMR chemical shifts of a series of 3d, 4d, and 5d transition-metal hydrides have revealed significant spin
orbit-induced heavy atom effects on the hydride shifts, in particular for several 4d and 5d complexes. The spin
orbit (SO) effects provide substantial, in some cases even the dominant, contributions to the well-known characteristic highfield hydride shifts of complexes with a partially filled d-shell, and thereby augment the Buckingham
Stephens model of off-center paramagnetic ring currents. In contrast, complexes with a 4d10 and 5d10 configuration exhibit large deshielding SO effects on their hydride 1H NMR shifts. The differences between the two classes of complexes are attributed to the dominance of π-type d-orbitals for the true transition-metal systems compared to σ-type orbitals for the d10 systems.

’ INTRODUCTION Transition-metal hydride complexes often play an important role as hydrogenation catalysts and/or act as key intermediates in C
H bond activation processes.1,2 The determination of their molecular and electronic structure is thus crucial, allowing deeper insight into the reaction mechanisms and aiding in the rational design of more efficient catalysts. Frequently, 1H NMR spectroscopy is the only experimental technique that indicates unambiguously the presence of a metal
hydrogen bond in a complex or cluster.3 Indeed, the hydride NMR chemical shifts provide a valuable source of structural information, as they reflect the electronic structure and bonding pattern at the metal center. The unusually negative 1H NMR chemical shifts of hydrogen atoms directly bonded to a transition metal center (with values ranging up to ca.
50 ppm in certain diamagnetic iridium complexes), and their dependence on the other ligands present at the metal site, have led Buckingham and Stephens to suggest an explanation model already in 1964.4,5 On the basis of ligandfield theory and the Ramsey formula of NMR chemical shifts,6 they argued that the local diamagnetic term of the hydride cannot account fully for such large shifts. Instead, paramagnetic ring currents within the incomplete valence d-shell of the transitionmetal site were invoked, which are experienced as an effective diamagnetic (diatropic in modern terminology) current at the off-center position of the hydrogen nucleus. Further, Buckingham r 2011 American Chemical Society

and Stephens predicted (erroneously, as we will show below) large shift anisotropies up to
500 ppm and found a dependence on M
H distances and on ligand-field strength of the trans ligand. Birnbaum criticized some of the explanations in terms of M
H distances and brought metal
ligand covalency (nephelauxetic effects) into play.7 More than 30 years after it was put forward, the off-center ring current model of Buckingham and Stephens has been essentially confirmed in density functional (DFT) calculations of a number of 3d carbonyl hydride complexes and of [HRe(CO)5] by Ruiz-Morales et al. in 1996.8 These calculations were, however, nonrelativistic except for the case of [HRe(CO)5], where approximate scalar relativistic corrections were applied. No spin
orbit coupling (SOC) was included, yet agreement with experiment was relatively good for the particular chosen set of complexes, with the largest deviation for the rhenium complex about 3 ppm for the isotropic shift. A computational study of 1H shifts in these and a few related transition-metal hydride complexes using DFT calculations has been reported recently also by del Rosal et al.,9 again without consideration of SOC effects. On the other hand, the last 20 years have seen a large number of quantitative computational studies indicating the appreciable Received: March 11, 2011 Revised: May 5, 2011 Published: May 17, 2011 5654

dx.doi.org/10.1021/jp202327z | J. Phys. Chem. A 2011, 115, 5654–5659

The Journal of Physical Chemistry A

ARTICLE

Figure 1. Schematic Structures of the Investigated Hydride Complexes (See Table 1 for R Substituents)

importance of SOC for NMR shifts of light nuclei bonded to heavy atoms (the “heavy-atom effect on the light-atom shielding” or “HALA” effect,10,11 which may even show up when the NMR nucleus is several bonds removed from the heavy atom). Due to the dominantly Fermi-contact-type (FC) mechanism of these SOC-induced HALA effects, 1H shifts are expected to be influenced particularly strongly, as hydrogen uses almost exclusively its 1s-orbital in bonding. This should provide a very efficient mechanism for the FC-type transfer of SOC effects. Extremely large SOC HALA effects have been found computationally not only for species like HI10,12 but also for 1H chemical shifts in mercury hydride complexes, RHgH.13,14 In the latter case, the SOC effects are strongly deshielding, and indeed the experimental shifts are dramatically positive. Closer analysis of computational studies carried out hitherto on SOC-induced HALA effects on NMR chemical shifts indicated that a dominant contribution of occupied orbitals with an approximate σ symmetry with respect to the bond between NMR nucleus and attached heavy atom will cause deshielding SOC HALA effects, whereas orbitals with approximate π-symmetry will cause shielding.15 The deshielding in the above-mentioned RHgH complexes falls into the former category. Given that Ruiz-Morales et al.8 invoke occupied dπ-type occupied orbitals in their paramagnetic high-field shift contributions for transition-metal hydrides, it is conceivable that similar orbitals may also cause additional SOC-induced high-field contributions to the 1H shifts (moderate but notable SOC high-field 13C shifts have been found previously for carbonyl ligands14,16). In the present study, we evaluate this assumption by a systematic comparison of relativistic four-component GIAO calculations, based on a recent efficient implementation of a matrix Dirac
Kohn
Sham approach,17,18 with scalar relativistic calculations on a series of transition-metal hydride complexes from the 3d, 4d, and 5d series (Figure 1). It is worth noting that most of these complexes are closely related to real catalytic systems, and this work represents the first fully relativistic study on chemical shifts of complexes of such size and importance. We include for comparison also a series of d10 complexes [HMPh] (M = Zn, Cd, Hg) and [HM(NHC)] (M = Cu, Ag, Au; NHC = N-heterocyclic carbene), with low-field 1H shifts (Figure 1). After completion of the present investigation, Bagno and Saielli19 reported a DFT study of methane activation by Rh

and Ir complexes. In DFT-GIAO calculations at the two-component ZORA level, they noted appreciable SOC effects on the 1 H hydride shifts in one rhodium and one iridium hydride complex, consistent with the present work. However, no systematic investigation regarding spin
orbit effects was included in their paper.

’ COMPUTATIONAL DETAILS The ground-state structures of all transition-metal hydrides were fully optimized at the restricted Kohn
Sham (KS) level using the hybrid B3LYP exchange-correlation functional,20 as implemented in the Gaussian program package.21 A quasirelativistic energy-adjusted small-core Stuttgart-type pseudopotential (effective-core potential, ECP) with corresponding (8s7p6d)/[6s5p3d] GTO valence basis set was used for the metal center,22 whereas ligand atoms were treated with the allelectron TZVP basis set.23 Analytical frequency calculations at the same level were used to verify the optimized structures to be minima on the potential-energy surface. In the case of complexes with bulky ligands containing side-chain alkyl or aryl groups, optimizations were performed for the full experimentally studied systems (cf. Table 1 and footnotes therein for R substituents). For the SCF and property calculations, however, these structures were subsequently simplified by replacing the R substituents with hydrogen atoms or methyl groups (cf. Table 1) using the standard bond lengths as listed in ref 24 (cf. Supporting Information for Cartesian coordinates). Fully relativistic density functional (DFT) calculations have been carried out at the matrix Dirac-Kohn
Sham (mDKS) level with the ReSpect-MAG code, including a new four-component module.25 Details of the mDKS-RMB-GIAO method are given in ref 25, and here we provide only the most salient features. This method combines the concept of gauge including atomic orbitals (GIAOs),26 with restricted magnetically balanced (RMB) orbitals for the small component.27 The large-component molecular B) , as orbitals (MOs) are expanded in GIAOs, χL(B λ M

LðB B, μ B Þ

ji 5655

¼

BÞ ∑λ CλiLðBB, μB ÞχLðB λ M

ð1Þ

dx.doi.org/10.1021/jp202327z |J. Phys. Chem. A 2011, 115, 5654–5659

The Journal of Physical Chemistry A

ARTICLE

Table 1. Comparison of Nonrelativistic (δNR), Scalar Relativistic (δ1c-DKH), and Fully Relativistic (δ4c-mDKS) Computed 1 H-NMR Chemical Shifts (in ppm relative to TMS) of Hydride Complexes with Experiment compound


[HCr(CO)5]




[HMo(CO)5] [HW(CO)5]
[HCrCp(CO)3] [HMoCp(CO)3] [HWCp(CO)3] [HMn(CO)5] [HTc(CO)5] [HRe(CO)5] [H2Fe(CO)4] [H2Ru(CO)4] [H2Os(CO)4] [HFe(CN)(dhpe)2] [HRu(CN)(dhpe)2] [HOs(CN)(dhpe)2] [HFeCl(dhpe)2] [HRuCl(dhpe)2] [HOsCl(dhpe)2] [HCo(CO)4] [HRh(CO)4] [HIr(CO)4] [HCo(CO)(PH3)3] [HRh(CO)(PH3)3] [HIr(CO)(PH3)3]

δNR δ1c-DKH Δδa δ4c-mDKS (ppm) (ppm) (ppm) (ppm)
5.6


5.6

þ0.1


2.7
2.1
4.7
3.8
3.6
5.7
3.2
2.7
6.4b
4.2b


2.7
2.1
4.7
3.8
3.6
5.7
3.2
2.6
6.4b
4.2b


0.1
0.7
0.8
2.1
4.1
0.6
1.1
1.6
1.4b
1.9b


3.5b
11.9
8.1
7.3
21.0
12.6
11.5
5.0
3.9
3.6
9.1
6.1
5.4


3.5b
12.0
8.2
7.6
21.0
12.8
12.2
5.0
4.0
3.6
9.2
6.3
5.9


3.7b
2.9
2.9
4.8
3.9
5.4
10.0
2.5
2.9
5.4
2.9
3.7
5.9

[HCoCl2(PMe3)2]
17.5
18.1
17.2 [HRhCl2(PMe3)2]
11.7
12.6
13.0 [HIrCl2(PMe3)2]
11.6
14.4
28.7 [HNiCl(PH3)2] [HPdCl(PH3)2] [HPtCl(PH3)2] [HCu(NHC)] [HAg(NHC)] [HAu(NHC)] [HZnPh] [HCdPh] [HHgPh]


10.2
10.5
7.6
3.7
4.2
6.0
3.4
4.4
10.1 þ1.4 þ1.3
0.1 þ2.6 þ2.5 þ1.0 þ0.9 þ0.6 þ5.1 þ4.7 þ4.8 þ0.9 þ4.7 þ5.0 þ3.6 þ3.8 þ4.7 þ11.7

in order to construct the small-component basis functions. Finally, the small component MOs are expanded as

δexpt. (ppm) (solvent)

1 ¼ 2c


5.5
6.9 (CD3CN)
7.0 (THF-d8)33
2.8
4.0 (CD3CN)32
2.9
4.2 (CD3CN)32
5.5
5.6 (C6D6)34
5.9
5.6 (THF-d8)35
7.8
7.4 (THF-d8)35
6.4
7.9 (C6D6)36
4.3
4.2
5.9 (hexane)37
7.8b
9.7 (THF-d8)38
6.1b
7.6 (pentane)39
7.9 (CD3CN)40 b
7.2
8.6 (C6D6)41
14.8
17.3 (C6D6)42,c
11.0
12.6 (C6D6)42,c
12.4
14.0 (C6D6)42,c
24.9
29.1 (C6D6)43,c
18.2
17.1 (CDCl3)44,c
22.2
22.8 (C6D6)45,c
7.5
11.6 (C6D6)46
6.9
9.0
12.1
12.1 (toluene)47,d
10.0
9.6 (C6D6)48,d
11.8
11.2 (CDCl3)49,d
10.3 (C6D6)50,d
35.3
25.6
31.1 (C6D6)51,e
43.2
49.2 (CDCl3)52,e
50.5 (toluene)53,e
18.1
23.0 (C6D6)54,f
10.2
14.0 (C6D6)54,f
14.5
17.0 (C6D6)54,f þ1.2 þ2.7 (C6D6)55,g þ3.5 þ5.7 þ5.1 (C6D6)56,g þ5.7 þ4.8 (C6D6)57,h þ8.6 þ6.8 (C6D6)57,i þ16.3 þ14.6 (C6D6)57

M

SðB B, μ B Þ

ji

M

SðB B, μ B Þ ðB BÞ Cλi ωλ

∑λ

M

ðB BÞ ðB μ 1 1 B B A þ σ B B A σ B3 B pþ σ c 3 0 c 3 0

32

a

Difference between one-component scalar relativistic and four-component fully relativistic results, as an estimate of SOC effects. b Results for axial and equatorial hydrogen atoms are averaged. c Experimental data for [HML(depe)2] (depe =1,2-bis(diethylphosphino)ethane). d Experimental data for [HM(CO)(PPh3)3]. e Experimental data for [HMCl2(PMe2tBu)2]. f Experimental data for [HMCl{P(CH2Ph)3}2]. g Experimental data for [HM(IPr)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). h Experimental value for [HZnPh]2. i Experimental value for a loosely associated dimer [HCdPh]2.

and the RMB ansatz is extended to GIAOs M

ðB BÞ ðB μ 1 1 1 σ B3 B pþ σ B3 B A0 þ σ B3 B A0 2c c c

Þ

! LðB BÞ

χλ

ð2Þ

!

Þ

χλ ð3Þ

B,μ BM ) B,μ BM) and CλiS(B represent the MO coefficients for Here, CLλi(B

the large and small component in the presence of the external magnetic field B B and the nuclear magnetic moment of Mth nucleus, μBM. χλ is an atomic orbital centered at a nucleus at RBλ and the associated GIAO is defined by   i LðB BÞ ðB BÞ Bλ
R χλ ¼ ωλ χλ ¼ exp
½BB  ðR B0 Þ 3 B r  χλ ð4Þ 2c The GIAO depends on the magnetic induction B B and the gauge origin R B0 through the phase factor ωλ. The NMR shielding tensor describes the leading-order response of the energy to an external magnetic field and a magnetic moment of the nucleus M M  d2 EðBB, Bμ Þ M ð5Þ σ uv ¼   dBu dμM M v B¼μ B B ¼0

The four-component mDKS calculations have been done at the generalized-gradient-approximation level (GGA) with the Becke exchange and Perdew correlation functionals (BP86).28 All-electron Hirao basis sets of the quality (20s15p9d), (21s19p12d), and (23s23p15d10f) were used for the 3d, 4d, and 5d metal centers, respectively.29 For ligand atoms we have employed fully uncontracted Huzinaga
Kutzelnigg-type IGLO-III basis sets.30 Fitting of the total electron density and of the components of the spin density was done with uncontracted auxiliary basis sets, constructed in a similar manner as in refs 18 and 31. Special attention was paid to the accuracy of numerical integration. In particular, the grid for numerical evaluation of integrals was denser in the core area. On heavy atom centers (Z > 18), we used a grid comprising 256 points in the radial quadrature and 110 points in the angular part, corresponding to ca. 28000 grid points per atom. A smaller integration grid with 128 radial shells was used for all other atoms. All relativistic calculations were done with a finite-size nucleus model employing the Gaussian charge distribution. For comparative purposes, and to extract SO contributions, one-component GIAO calculations of 1H NMR chemical shifts were also done in the MAG code, using the same basis sets and functional as the mDKS calculations, without and with including the scalar relativistic effects via the Douglas
Kroll
Hess (DKH) Hamiltonian. The computed nuclear shieldings were converted to chemical shifts (δ, in ppm) relative to the shielding of tetramethylsilane (TMS), obtained at the same computational level.

’ RESULTS AND DISCUSSION The results of nonrelativistic (NR), scalar relativistic onecomponent (1c-DKH) and fully relativistic four-component calculations (4c-mDKS) of hydride 1H NMR chemical shifts are compared to experimental data in Table 1. The comparison is further illustrated in Figure 2, where it becomes particularly obvious, that the NR and 1c-DKH results without inclusion of 5656

dx.doi.org/10.1021/jp202327z |J. Phys. Chem. A 2011, 115, 5654–5659

The Journal of Physical Chemistry A SOC terms tend to be insufficiently negative for the true transition-metal systems featuring the most negative 1H isotropic shifts and insufficiently positive for the 4d10 and 5d10 systems. This is improved significantly in all cases by inclusion of SOC effects in the four-component fully relativistic calculations, which therefore agree much better with experiment. Some of the systems exhibit small SOC effects (see below), and thus oneand four-component results agree much better in those cases (Table 1 and Figure 2). The fact that most of the differences between the one- and four-component data arise indeed from the neglect of SOC effects in the former has been confirmed independently by a third-order perturbation treatment of the SOC effects based on one-component calculations (see Table S1 in Supporting Information). In general, all complexes with a partially filled d-shell exhibit negative (high-field) hydride NMR shifts. This phenomenon is reproduced qualitatively already by the nonrelativistic and/or onecomponent scalar relativistic results, confirming the rationalization by paramagnetic currents in the Buckingham
Stephens model. However, these calculations do not correctly describe the trend from the 3d to the 5d complexes within a given isoelectronic

Figure 2. Comparison of calculated hydride 1H NMR chemical shifts obtained by nonrelativistic (1c-NR), scalar relativistic (1c-DKH), and fully relativistic (4c-mDKS) methods. The dashed line represents the ideal agreement with experiment.

ARTICLE

series, as shown in Figure 3. The experimentally observed “Λshape” behavior, including a sharp drop of hydride 1H shifts from 4d to 5d series, is reproduced only by the fully relativistic calculations. While the nonmonotonous behavior was already noticed by Buckingham and Stephens, they rationalized it by different M
H bond lengths in the 4d and 5d hydride complexes.4,5 However, the M
H bond lengths in these two series of transition metal complexes differ by less than 4 pm (cf. Table S2 in Supporting Information). As an increase of the M
H bond length by 5 pm would reduce the hydridic shift by ca. 1 ppm (cf. Table S3 in Supporting Information), the argumentation of Buckingham and Stephens seems to be incorrect. Instead, the fact that the fully relativistic four-component calculations reproduce the trend while one-component calculations do not indicates the SOC origin of the“Λ-shape” behavior and disproves the original ligand-field and distance arguments (Figure 3). We note in passing, that the same ligand-field d-orbital-type MOs that dominate the Buckingham
Stephens terms are also largely responsible for the SOC contributions. Similarly, the SOC origin of the unusual low-field shifts of d10 hydrides, which had already been demonstrated for mercury complexes,13,14 is confirmed here also for the other d10 species, in particular for the gold complex. We note furthermore that the data in Table 1 reveal also the appreciable importance of the nature of the other ligands, in particular of the trans ligand, which had already been discussed in the original papers.4,5 However, it is obvious that the SO effects, neglected in the Buckingham
Stephens model, play an important role also here. Interestingly, the SO effects are more dramatic in complexes with trans ligands of lower-field strength (see, e.g., [HMCl(dhpe)2] vs [HM(CN)(dhpe)2]). Taking the SO effects into account may indeed allow us to examine the effect of the trans ligand more thoroughly. The ligand effects are currently examined in our laboratories in more detail and results will be reported elsewhere. No experimental shift tensors are available for transition-metal hydrides. Nevertheless, we provide the shielding tensors as predictions in Supporting Information (Table S4) and note that for a given vertical series of carbonyl complexes, the scalar relativistic results change from a negative shielding anisotropy for a given 3d complex to increasingly positive values for the 4d

Figure 3. Comparison of scalar relativistically (1c-DKH) and fully relativistically (4c-mDKS) computed hydride 1H NMR chemical shifts with experimental data for selected isoelectronic 3d
5d series. 5657

dx.doi.org/10.1021/jp202327z |J. Phys. Chem. A 2011, 115, 5654–5659

The Journal of Physical Chemistry A and 5d complexes. This is mainly related to a decrease of the (in all cases shielding) Buckingham
Stephens-type paramagnetic contributions to the perpendicular components, likely due to an increase of the ligand-field splitting down a given group (leading to enhanced energy denominators). Turning to the fully relativistic results, the spin
orbit contributions enhance the perpendicular shielding and thus the positive anisotropies further for the 4d and particularly the 5d complexes. The anisotropies are generally more negative for the phosphane-substituted group 9 complexes already at the one-component level, due to the very pronouncedly shielding ring-current contributions to the perpendicular components. These and the negative anisotropies are further enhanced at the four-component level. The tensors for the d10 complexes differ completely from this behavior (Table S4, Supporting Information). As the background for this behavior has already been discussed in detail for organomercury hydrides in ref 13, we will refrain here from a closer discussion.

’ CONCLUSIONS The Buckingham
Stephens model of off-center paramagnetic ring currents to explain the characteristic and important high-field 1H shifts of transition-metal hydride complexes remains valid but has to be augmented by consideration of sizable spin
orbit effects, particularly for 4d and 5d complexes. The spin
orbit contributions affect mainly the perpendicular shielding tensor contributions, thereby enhancing the “Buckingham
Stephens-type” terms. As the dependence of the spin
orbit terms on the presence of low-lying excited states of the system differs from that of the nonrelativistic shielding terms, a detailed analysis of those factors that determine the shift tensors in detail throughout the transition-metal series will be the interesting topic of our ongoing work, together with an unraveling of the detailed origin of trans and cis ligand effects. The direct comparison of the true transition-metal hydride complexes with incomplete metal d-shell to d10 systems of groups 11 and 12 is particularly revealing. The latter systems lack not only the Buckingham
Stephens-type terms but exhibit large, and again characteristic, deshielding spin
orbit contributions, again for the perpendicular tensor components, as we had shown previously for the special case of organomercury hydrides. The shielding spin
orbit contributions of the “true” transitionmetal hydrides arise from occupied π-type metal d-orbitals, whereas occupied σ-type orbitals dominate the deshielding spin
orbit contributions to the hydride shifts of d10 complexes. ’ ASSOCIATED CONTENT

bS

Supporting Information. Cartesian coordinates of the optimized structures, computed 1H NMR chemical shielding tensor anisotropies, and more detailed analysis. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; [email protected].

’ ACKNOWLEDGMENT This work has been supported by the Berlin cluster of excellence on “Unified Concepts in Catalysis” (UniCat) and Slovak

ARTICLE

grant agencies VEGA (Grant No. 2/0079/09) and APVV (Grant No. VVCE-0004-07). P.H. gratefully acknowledges the Alexander von Humboldt Foundation for a research fellowship.

’ REFERENCES (1) For reviews, see for example:Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507–514. Balcells, D.; Clot, E.; Eisenstein, O. Chem. Rev. 2010, 110, 749–823. Shilov, A. E.; Shulpin, G. B. Chem. Rev. 1997, 97, 2879–2932. Kaesz, H. D.; Saillant, R. B. Chem. Rev. 1972, 72, 231–281. Samec, J. S. M.; Backvall, J. E.; Andersson, P. G.; Brandt, P. Chem. Soc. Rev. 2006, 35, 237–248. Jones, W. D. Acc. Chem. Res. 2003, 36, 140–146. Backvall, J. E. J. Organomet. Chem. 2002, 652, 105–111. Jia, C. G.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633–639. (2) For recent examples, see:Lin, S. B.; Day, M. W.; Agapie, T. J. Am. Chem. Soc. 2011, 133, 3828–3831. Ledger, A. E. W.; Moreno, A.; Ellul, C. E.; Mahon, M. F.; Pregosin, P. S.; Whittlesey, M. K.; Williams, J. M. J. Inorg. Chem. 2010, 49, 7244–7256. Boddien, A.; Loges, B.; Gartner, F.; Torborg, C.; Fumino, K.; Junge, H.; Ludwig, R.; Beller, M. J. Am. Chem. Soc. 2010, 132, 8924–8934. Federsel, C.; Jackstell, R.; Beller, M. Angew. Chem., Int. Ed. 2010, 49, 6254–6257. Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc. 2009, 131, 14168–14169. Rubio, M.; Suarez, A.; del Rio, D.; Galindo, A.; Alvarez, E.; Pizzano, A. Organometallics 2009, 28, 547–560. Casey, C. P.; Guan, H. R. J. Am. Chem. Soc. 2009, 131, 2499–2507. Martinez, R.; Simon, M. O.; Chevalier, R.; Pautigny, C.; Genet, J. P.; Darses, S. J. Am. Chem. Soc. 2009, 131, 7887–7895. Lee, J. P.; Ke, Z. F.; Ramirez, M. A.; Gunnoe, T. B.; Cundari, T. R.; Boyle, P. D.; Petersen, J. L. Organometallics 2009, 28, 1758–1775. Torres, O.; Martin, M.; Sola, E. Organometallics 2009, 28, 863–870. Garcia-Anton, J.; Axet, M. R.; Jansat, S.; Philippot, K.; Chaudret, B.; Pery, T.; Buntkowsky, G.; Limbach, H. H. Angew. Chem., Int. Ed. 2008, 47, 2074–2078. Douglas, T. M.; Brayshaw, S. K.; Dallanegra, R.; Kociok-Kohn, G.; Macgregor, S. A.; Moxham, G. L.; Weller, A. S.; Wondimagegn, T.; Vadivelu, P. Chem.—Eur. J. 2008, 14, 1004–1022. Liang, L. C.; Chien, P. S.; Lee, P. Y. Organometallics 2008, 27, 3082–3093. (3) Morris, R. H. Coord. Chem. Rev. 2008, 252, 2381–2394. (4) Buckingham, A. D.; Stephens, P. J. J. Chem. Soc. 1964, 2747– 2759. (5) Buckingham, A. D.; Stephens, P. F. J. Chem. Soc. 1964, 4583– 4587. (6) Ramsay, N. F. Phys. Rev. 1950, 78, 699–703. (7) Birnbaum, E. R. Inorg. Nucl. Chem. Lett. 1971, 7, 233–237. (8) Ruiz-Morales, Y.; Schreckenbach, G.; Ziegler, T. Organometallics 1996, 15, 3920–3923. (9) del Rosal, I.; Maron, L.; Poteau, R.; Jolibois, F. Dalton Trans. 2008, 3959–3970. (10) Pyykk€o, P.; G€orling, A.; R€osch, N. Mol. Phys. 1987, 61, 195–205. (11) Kaupp, M.; Malkina, O. L.; Malkin, V. G.; Pyykk€o, P. Chem.— Eur. J. 1998, 4, 118–126. (12) Morishima, I.; Endo, K.; Yonezawa, T. J. Chem. Phys. 1973, 59, 3356–3364. (13) Kaupp, M.; Malkina, O. L. J. Chem. Phys. 1998, 108, 3648–3659. (14) Vaara, J.; Malkina, O. L.; Stoll, H.; Malkin, V. G.; Kaupp, M. J. Chem. Phys. 2001, 114, 61–71. (15) Kaupp, M. Relativistic Effects on NMR Chemical Shifts. In Relativistic Electronic Structure Theory II: Applications; Schwerdtfeger, P., Ed.; Elsevier: Amsterdam, 2004; Chapter 9, pp 552
597. (16) Wolff, S. K.; Ziegler, T. J. Chem. Phys. 1998, 109, 895–905. (17) Komorovsky, S.; Repisky, M.; Malkina, O. L.; Malkin, V. G.; Ondik, I. M.; Kaupp, M. J. Chem. Phys. 2008, 128, 104101. (18) Komorovsky, S.; Repisky, M.; Malkina, O. L.; Malkin, V. G. J. Chem. Phys. 2010, 132, 154101. (19) Bagno, A.; Saielli, G. Phys. Chem. Chem. Phys. 2011, 13, 4285– 4291. (20) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623–11627. 5658

dx.doi.org/10.1021/jp202327z |J. Phys. Chem. A 2011, 115, 5654–5659

The Journal of Physical Chemistry A (21) Frisch, M. J.; et al. Gaussian 09, revision A.02; Gaussian, Inc.: Wallingford, CT, 2009. (22) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987, 86, 866–872. Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123–141. (23) Sch€afer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829–5835. (24) Pyykk€o, P.; Atsumi, M. Chem.—Eur. J. 2009, 15, 186–197. (25) Malkin, V. G.; Malkina, O. L.; Reviakine, R.; Arbuznikov, A. V.; Kaupp, M.; Schimmelpfennig, B.; Malkin, I.; Repisky, M.; Komorovsky, S.; Hrobarik, P.; Malkin, E.; Helgaker, T.; Ruud, K. MAG-ReSpect, version 2.3, 2010 (26) Hansen, A. E.; Bouman, T. D. J. Chem. Phys. 1985, 82, 5035– 5047. (27) Aucar, G. A.; Saue, T.; Visscher, L.; Jensen, H. J. A. J. Chem. Phys. 1999, 110, 6208–6218. Kutzelnigg, W. J. Comput. Chem. 1999, 20, 1199–1219. (28) Becke, A. D. Phys. Rev. A 1988, 38, 3098–3100. Perdew, J. P.; Wang, Y. Phys. Rev. B 1986, 33, 8822–8824. Perdew, J. P.; Wang, Y. Phys. Rev. B 1986, 34, 7406. (29) Tsuchiya, T.; Abe, M.; Nakajima, T.; Hirao, K. J. Chem. Phys. 2001, 115, 4463–4472. (30) Kutzelnigg, W.; Fleischer, U.; Schindler, M. The IGLO-Method: Ab Initio Calculation and Interpretation of NMR Chemical Shifts and Magnetic Susceptibilities. In NMR Basic Principles and Progress; Diehl, P., Fluck, E., G€unther, H., Kosfeld, R., Seelig, J., Eds.; Springer Verlag: Berlin/ Heidelberg, 1991; Vol. 23, pp 165
262. (31) Hrobarik, P.; Repisky, M.; Komorovsky, S.; Hrobarikova, V.; Kaupp, M. Theor. Chem. Acc. 2011, 129, 715
725. (32) Darensbourg, M. Y.; Slater, S. J. Am. Chem. Soc. 1981, 103, 5914–5915. (33) Brunet, J. J.; Diallo, O.; Donnadieu, B.; Roblou, E. Organometallics 2002, 21, 3388–3394. (34) Ng, V. W. L.; Kuan, S. L.; Weng, Z.; Leong, W. K.; Vittal, J. J.; Koh, L. L.; Tan, G. K.; Goh, L. Y. J. Organomet. Chem. 2005, 690, 2323–2332. (35) Mahmoud, K. A.; Rest, A. J.; Alt, H. G. J. Chem. Soc., Dalton Trans. 1984, 187–197. (36) Bullock, R. M.; Rappoli, B. J. J. Organomet. Chem. 1992, 429, 345–368. (37) Byers, B. H.; Brown, T. L. J. Am. Chem. Soc. 1977, 99, 2527–2532. (38) Krusic, P. J.; Jones, D. J.; Roe, D. C. Organometallics 1986, 5, 456–460. (39) Cotton, J. D.; Bruce, M. I.; Stone, F. G. A. J. Chem. Soc. A 1968, 2162–2165. (40) Moore, E. J.; Sullivan, J. M.; Norton, J. R. J. Am. Chem. Soc. 1986, 108, 2257–2263. (41) Carter, W. J.; Kelland, J. W.; Okrasinski, S. J.; Warner, K. E.; Norton, J. R. Inorg. Chem. 1982, 21, 3955–3960. (42) Rocchini, E.; Rigo, P.; Mezzetti, A.; Stephan, T.; Morris, R. H.; Lough, A. J.; Forde, C. E.; Fong, T. P.; Drouin, S. D. J. Chem. Soc. Dalton 2000, 3591–3602. (43) Chatt, J.; Hayter, R. G. J. Chem. Soc. 1961, 5507–5511. (44) Chatt, J.; Hayter, R. G. J. Chem. Soc. 1961, 2605–2611. (45) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J.; Morris, R. H.; Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J. Am. Chem. Soc. 1996, 118, 5396–5407. (46) Bianchi, M.; Frediani, P.; Piacenti, F.; Rosi, L.; Salvini, A. Eur. J. Inorg. Chem. 2002, 1155–1161. (47) Gusev, D. G.; Vymenits, A. B.; Bakhmutov, V. I. Inorg. Chem. 1991, 30, 3116–3118. (48) Trzeciak, A. M.; Ziolkowski, J. J. J. Organomet. Chem. 1992, 429, 239–244. (49) Bath, S. S.; Vaska, L. J. Am. Chem. Soc. 1963, 85, 3500–3501. (50) Ainscough, E. W.; Robinson, S. D.; Levison, J. J. J. Chem. Soc. A 1971, 3413–3424. (51) Wang, K.; Goldman, M. E.; Emge, T. J.; Goldman, A. S. J. Organomet. Chem. 1996, 518, 55–68.

ARTICLE

(52) Mura, P. J. Coord. Chem. 2000, 51, 253–260. (53) Empsall, H. D.; Hyde, E. M.; Mentzer, E.; Shaw, B. L.; Uttley, M. F. J. Chem. Soc. Dalton 1976, 2069–2074. (54) Seligson, A. L.; Cowan, R. L.; Trogler, W. C. Inorg. Chem. 1991, 30, 3371–3381. (55) Mankad, N. P.; Laitar, D. S.; Sadighi, J. P. Organometallics 2004, 23, 3369–3371. (56) Tsui, E. Y.; Muller, P.; Sadighi, J. R. Angew. Chem., Int. Ed. 2008, 47, 8937–8940. Escalle, A.; Mora, G.; Gagosz, F.; Mezailles, N.; Le Goff, X. F.; Jean, Y.; Le Floch, P. Inorg. Chem. 2009, 48, 8415–8422. (57) Zhu, Z.; Brynda, M.; Wright, R. J.; Fischer, R. C.; Merrill, W. A.; Rivard, E.; Wolf, R.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2007, 129, 10847–10857.

’ NOTE ADDED AFTER ASAP PUBLICATION This paper was published ASAP on May 17, 2011 with an incorrect Supporting Information file. The corrected version was published ASAP on June 2, 2011.

5659

dx.doi.org/10.1021/jp202327z |J. Phys. Chem. A 2011, 115, 5654–5659