Nature of M–E Bonds in Metallosilylenes, -germylenes, -stannylenes

ARTICLE pubs.acs.org/Organometallics

Nature of M
E Bonds in Metallosilylenes, -germylenes, -stannylenes, and -plumbylenes [(η5-C5H5)(Me3P)(H)2M(EPh)] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb) Krishna K. Pandey*,† and Philip P. Power‡ † ‡

School of Chemical Sciences, Devi Ahilya University Indore, Indore 452 017, India Departament of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States

bS Supporting Information ABSTRACT: Geometry, electronic structure, and bond energy analysis of M
ER bonds in the terminal metallosilylenes, metallogermylenes, metallostannylenes, and metalloplumbylenes of iron, ruthenium, and osmium [(η5-C5H5)(Me3P)(H)2M(EPh)] (I, M = Fe, E = Si; II, M = Fe, E = Ge; III, M = Fe, E = Sn; VI, M = Fe, E = Pb; V, M = Ru, E = Si; VI, M = Ru, E = Ge; VII, M = Ru, E = Sn; VIII, M = Ru, E = Pb; IX, M = Os, E = Si; X, M = Os, E = Ge; XI, M = Os, E = Sn; XII, M = Os, E = Pb) were investigated at the DFT/BP86/TZ2P/ZORA level of theory. The M
E bonds in these complexes are essentially M
E single bonds. In all studied complexes, the π-bonding contribution to the total M
EPh bond is significantly smaller than that of the σ-bonding and increases upon going from M = Fe to Os. Thus, in the EPh ligands the E atom is predominantly a σ-donor. The nature of E has a significant effect on the M
P bonding to the Me3P ligand trans to EPh. The M
P bond distances decrease upon going from SiPh to PbPh. The contributions of the electrostatic interactions ΔEelstat to the M
EPh bonds are larger in all complexes I
XII than the covalent bonding ΔEorb. The M
E bond in each case has a degree of covalent character of between 36% and 48%. In contrast to the interaction between charged fragments, where the electrostatic interactions ΔEelstat are greater that the orbital interactions ΔEorb, the orbital interactions ΔEorb are larger than the electrostatic interactions ΔEelstat for interaction between neutral fragments. In the case of homolytic bond dissociation, the M
E bond in each case has a degree of covalent character of between 56% and 64%.

1. INTRODUCTION Since the first report of stable germylenes and stannylenes by Lappert and co-workers in 1976,1 much attention has been paid to low-valent silylenes (:SiR2), germylenes (:GeR2), stannylenes (:SnR2), and plumbylenes (:PbR2).2
12 The ground state of : ER2 (E = Si, Ge, Sn, Pb) is a singlet, unlike :CR2, where the ground state is often a triplet. Substitution of one of the substituents R with a metal fragment results in the formation of metallosilylenes, -germylenes, -stannyles, and -plumbylenes. Recently compounds [LnM(ER)] (E = Ge, Sn, Pb), which have a strongly bent M
E
R linkage (Chart 1), were synthesized. Jutzi and Leue13 isolated the first examples of iron-germylenes [(η5-C5R5)(CO)2Fe-GeC6H2-2,4,6-tBu3] (R = H, Me), but no structures have been determined. Power and co-workers reported the first structurally characterized representative examples of metallogermylenes, metallostannylenes, and metalloplumbylenes of formula (η5-C5H5)(CO)3ME(C6H3-2,6(C6H2-2,4,6-iPr3)2 (M = Cr, W; E = Ge;14 M = Cr, Mo, or W;15a E = Sn;15 M = Mo or W; E = Pb).14,15 The M
E
R bond angles in these complexes lie between 106.7
and 117.8
. Tilley and coworkers16 reported the osmium metallostannylene complex [(η5-C5Me5)(H)2Os-SnC6H2-2,4,6-iPr3], but no structure has been determined. The related complexes [(η5-C5H5)(CO)2FeE{(NC(C6H3-2,6-iPr2)CMe}2CH] (E = Ge or Sn), featuring divalent Ge and Sn substituted by a bidentate β-diketiminate r 2011 American Chemical Society

ligand, have been reported by Inoue and Driess.17 To best of our knowledge, no base-free metallocarbenes and metallosilylenes containing M
ER (E = C, Si) groups are currently known. This may be related to the lower stability of carbenes and silylenes. Nonetheless, numerous carbenes18
29 and silylenes2 have been stabilized, and it is likely that metallocarbenes and metallosilylenes will be isolated in the future. Pandey and co-workers reported geometries and bonding energy analyses of metallosilylenes, metallogermylenes, metallostannylenes, and metalloplumbylenes of chromium, molybdenum, tungsten, and iron by theoretical studies.30,31 To the best of our knowledge, the structure and M
ER bonding analysis of the terminal neutral metallo-ylene complexes of iron, ruthenium, and osmium have not been studied computationally. Here, for the first time, we report the geometry and electronic structure, as well as nature, of M
ER bonds in the terminal metallosilylenes, metallogermylenes, metallostannylenes, and metalloplumbylenes of iron, ruthenium, and osmium [(η5-C5H5)(Me3P)(H)2M(EPh)] (I, M = Fe, E = Si; II, M = Fe, E = Ge; III, M = Fe, E = Sn; VI, M = Fe, E = Pb; V, M = Ru, E = Si; VI, M = Ru, E = Ge; VII, M = Ru, E = Sn; VIII, M = Ru, E = Pb; IX, M = Os, E = Si; X, M = Os, E = Ge; XI, M = Os, E = Sn; XII, M = Os, E = Pb). Received: March 23, 2011 Published: May 25, 2011 3353

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Chart 1. Overview of Experimentally Known Heavy Metallo-ylidenes

Figure 1. (a) Schematic representation of the orbital interactions between closed-shell metal fragments [M]
and ligands ERþ. The M
ER bonding has two components, i.e., the σ donation from the occupied metal dz2 and dyz orbitals into the in-plane p(π) atomic orbitals (AO) of Si, Ge, Sn, and Pb and π^ donation from the occupied metal dxz orbital into the out-of-plane p(π) atomic orbital of Si, Ge, Sn, and Pb. (b) Orbital interactions between neutral fragments [M] and ER (doublet state) with shared electron metal dz2
p(π) atomic orbitals of Si, Ge, Sn, and Pb and π^ donation from the occupied metal dxz orbital into the out-of-plane p(π) atomic orbital of Si, Ge, Sn, and Pb.

2. COMPUTATIONAL METHODS

As mentioned above, synthesis of the osmium metallostannylene complex [(η5-C5Me5)(H)2Os-SnC6H2-2,4,6-iPr3], without structural data, has been reported.16 Therefore, we planed to determine the optimized geometry of studied complexes and to analyze the nature of M
E bonds. A more detailed understanding of the structure and bonding in metallosilylenes, metallogermylenes, metallostannylenes, and metalloplumbylenes complexes is a requisite, particularly for the synthesis of terminal transition metalloylenes. In the model complexes, the bulky substituents at silicon, germanium, tin, and lead atoms are replaced by a phenyl group. We report on the energy decomposition analysis of the M
ER bonds, which gives the energies that are associated with the σ-bonding and π-bonding (see Figure 1 for schematic presentation of the M
ER bond). The relative strength of the electrostatic and covalent contributions to the bond strength is also reported. We investigated the influence of the variation of the group 14 element on the nature of the transition metal main group single bond. In effect, the main goals of the present study are (i) to determine the structures and to analyze the nature of M
E bonds in metallosilylenes, metallogermylenes, metallostannylenes, and metalloplumbylenes, (ii) to elucidate the role of the transition metal atoms and E atom of EPh ligands in the stability of the M
ER, M
H, and M
P bonds, and (iii) to determine the contributions of the M
ER σ-bonding and M
ER π-bonding to the total MtER and M
ER bonding energies.

Calculations of the model complexes have been performed at the nonlocal DFT level of theory using the exchange functional of Becke32 and the correlation functional of Perdew33,34 (BP86). Scalar relativistic effects have been considered using the ZORA formalism.35 Uncontracted Slater-type orbitals (STOs) using triple-ζ basis sets augmented by two sets of polarization functions were employed for the SCF calculations. 36 The (n
1)s2 and the (n
1)p6 core electrons of the main group elements, (1s2s2p)10 core electrons of iron, (1s2s2p3s3p3d)28 core electrons of ruthenium, (1s2s2p3s3p3d4s4p4d)36 core electrons of tin, and (1s2s2p3s3p3d4s4p4d)46 core electrons of lead and osmium were treated by the frozen-core approximation.37 An auxiliary set of s, p, d, f, and g STOs was used to fit the molecular densities and to present the Coulomb and exchange potentials accurately in each SCF cycle.38
43 A numerical integration accuracy of INTEGRATION=5 was used throughout. Frequency calculations were performed to determine whether the optimized geometries were minima on the potential energy surface. The calculations were performed utilizing the program package ADF-2009.01.44 The electronic structures of the complexes (I
VIII) were examined by NBO analysis.45 The molecular orbitals were constructed using the MOLDEN program.46 The bonding interactions between metal fragments [(η5-C5H5)(Me3P)(H)2M]
(M = Fe, Ru, Os) and ligand fragments [EPh]þ (E = Si, Ge, Sn, Pb) (singlet states) as well as the neutral fragments [(η5-C5H5)(Me3P)(H)2M] and [EPh], both in their electronic and geometric most stable (doublet states) forms, have been analyzed with Cs symmetry using the energy decomposition scheme of the program package ADF, which is based on the work by Morokum47 and Ziegler and Rauk.48 It has been shown that the results of the energy decomposition analysis (EDA) analyses give a quantitative insight into the nature of the metal
ligand interactions.30,31,49
55 Details of the EDA method are given elsewhere.30 The covalent bond character = ΔEorb/(ΔEorb þ ΔEelstat).

3. RESULTS AND DISCUSSION 3.1. Geometries. The important optimized bond distances and bond angles of the metallo-ylenes I
XII at the BP86/TZ2P/ ZORA level of theory are presented in Table 1. The structures of [(η5-C5H5)(Me3P)(H)2M(SnPh)] (M = Fe, Ru, Os) (i.e., complexes III, VII, and XI) are shown in Figure 2. The structures of the related complexes with E = Si, Ge, Pb are similar to those presented in this figure and are therefore not included. Cartesian 3354

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Table 1. Selected Optimized Geometrical Parameters for Metallo-ylenes [(η5-C5H5)(Me3P)(H)2M
EPh] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb) bond distances (Å) M
E

E
C

M
H

M
P

bond angles (deg) E
H

M
E
C

E
M
H

H
M
H

E
M
P

P
M
H

[(η5-C5H5)(Me3P)(H)2Fe-SiPh]

2.356

1.933

1.587

2.192

1.732

101.7

47.3

94.2

95.8

90.4

[(η5-C5H5)(Me3P)(H)2Fe-GePh]

2.452

2.046

1.585

2.175

1.863

97.4

49.4

98.0

96.9

89.8

[(η5-C5H5)(Me3P)(H)2Fe-SnPh] [(η5-C5H5)(Me3P)(H)2Fe-PbPh]

2.590 2.674

2.253 2.362

1.559 1.550

2.159 2.147

2.157 2.312

99.7 100.1

56.3 59.5

106.0 107.7

101.9 104.4

83.5 80.5

[(η5-C5H5)(Me3P)(H)2Ru-SiPh]

2.428

1.935

1.676

2.285

1.845

101.2

49.4

97.5

93.7

86.5

[(η5-C5H5)(Me3P)(H)2Ru-GePh]

2.503

2.049

1.655

2.262

2.080

97.9

55.6

106.2

96.6

82.0

[(η5-C5H5)(Me3P)(H)2Ru-SnPh]

2.667

2.256

1.649

2.264

2.321

99.2

59.6

108.1

101.1

78.8

[(η5-C5H5)(Me3P)(H)2Ru-PbPh]

2.759

2.359

1.649

2.259

2.427

98.7

60.8

107.8

102.8

77.6

[(η5-C5H5)(Me3P)(H)2Os-SiPh]

2.402

1.943

1.650

2.289

2.211

103.7

63.0

113.7

99.8

77.2

[(η5-C5H5)(Me3P)(H)2Os-GePh]

2.504

2.059

1.652

2.278

2.324

100.1

64.2

114.5

101.0

76.6

[(η5-C5H5)(Me3P)(H)2Os-SnPh] [(η5-C5H5)(Me3P)(H)2Os-PbPh]

2.686 2.781

2.265 2.371

1.655 1.657

2.283 2.278

2.475 2.542

100.1 99.1

64.5 64.2

112.3 111.1

104.3 105.6

76.4 76.7

Figure 2. Optimized geometries of the metallo-ylidenes [(η5-C5H5)(Me3P)(H)2M
SnPh] (M = Fe, Ru, Os). The most important bond distances and angles are given in Table 1.

coordinates of all studied complexes are given in the Supporting Information. As mentioned above, the metallo-ylene complex of ruthenium studied in this paper is unknown, and the X-ray structures of the metallogermylene derivatives of iron13 [(η5-C5R5)(CO)2FeGeC6H2-2,4,6-tBu3] (R = H, Me) and metallostannylene derivative of osmium16 [(η5-C5Me5)(H)2Os-SnC6H2-2,4,6-iPr3] are unavailable. Therefore, we are unable compare the calculated values of the complexes I
XII with the experimental data. As summarized in Table 1, the M
E bond distances in the complexes (I
XII) are slightly longer than those expected for M
E single bonds estimated on the basis of covalent radii predictions (Fe
Si = 2.32 Å, Fe
Ge = 2.37 Å, Fe
Sn = 2.56 Å, Fe
Pb = 2.60 Å, Ru
Si = 2.41 Å, Ru
Ge = 2.46 Å, Ru
Sn = 2.65 Å, Ru
Pb = 2.69 Å, Os
Si = 2.45 Å, Os
Ge = 2.50 Å, Os
Sn = 2.69 Å, Os
Pb = 2.73 Å),56 which suggests that M
E bonds are essentially single ones. Upon going from M = Fe to M = Os, the calculated M
E bond distances increase, in most cases, in the order 2.356 Å (I) < 2.428 Å (V) > 2.402 Å (IX); 2.452 Å (II) < 2.503 Å (VI) < 2.504 Å (X); 2.590 Å (III) < 2.667 Å (VII) < 2.686 Å (XI); 2.674 Å (IV) < 2.759 Å (VIII) < 2.781 Å (XII). On going from metallosilylenes to metalloplumbylenes, we note a steady increase in the M
E bond distance. The bent coordination geometries at silicon, tin, and lead (M
E
C bond angles in the range 97.4
103.7
) in these compounds are consistent with the presence of divalent Si(II), Ge(II), Sn(II), and Pb(II) atoms, which are singly bonded to a transition metal and the carbon of a phenyl group. The optimized Si
C, Ge
C, Sn
C, and Pb
C bond distances in I
XII (see Table 1) are similar to those expected for a single bond based on covalent radii predictions (Si
C = 1.91 Å, Ge
C = 1.96 Å, Sn
C = 2.15 Å, Pb
C = 2.19 Å).56 The Ge
C, Sn
C, and Pb
C bond lengths and M
E
C bond angles in metallogermylenes, metallostannylenes, and metalloplumbylenes are within the known range for mononuclear stannylenes and plumbylenes (see Chart 1).14,15 Hence, the calculated geometries of the compounds I
XII agree with those of the known structures of metallogermylenes, stannylenes, and plumbylenes that have one metal fragment as a substituent. Furthermore, the nature of the EPh ligands has a significant effect on the metal coordination geometry of complexes I
XII. 3355

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Figure 3. Calculated NPA charges of the metallo-ylenes [(η5-C5H5)(Me3P)(H)2M
EPh] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb). The values in parentheses are Wiberg bond indices (WBI).

The M
P bond distances, bonds trans to EPh, decrease upon going from SiPh to PbPh (see Supporting Information Figure 1S). On the other hand, the E
M
H and E
M
P bond angles, in all three sets of complexes, increase upon going from silylenes to plumbylenes (see Supporting Information Figure 2S). 3.2. Bonding Analysis of the M
EPh Bonds of the Complexes I
XII. We begin the analysis of the M
E bonding in the metallo-ylenes I
XII with a discussion of bond orders and atomic charges. The Wiberg bond indices (WBI)57 and natural population analysis (NPA) charge distributions are given in Figure 3. As seen in Figure 3, the WBI values of the M
E bonds in the complexes I
XII are significantly smaller (0.36
0.66), indicating a nearly M
E single bond. Upon going from M = Fe to M = Os, the WBI values of the M
E bonds increase as 0.36 (I) < 0.43 (V) < 0.63 (IX), 0.40 (II) < 0.48 (VI) < 0.63 (X), 0.48 (III) < 0.57 (VII) < 0.66 (XI), 0.47 (IV) ∼ 0.46 (VIII) < 0.55 (XII). The bond indices of the E
-C(Ph) (0.68
0.78) in these complexes (I
XII) are not very different. The WBI values for

Pb
C are lowest because of the inertness of s electrons on Pb. Relativistic contraction of the 6s electrons of Pb tend to draw the electrons closer to the nucleus. Thus, the lone pair resides primarily in the 6s orbital. The presence of a nonbonding lone pair leads to exclusion of 6s electrons from bonding, and this exclusion is a leading cause of the decrease in Pb
C bond strength. Like the WBI of the Pb
C bond, WBI of the Pb
M bond is not the lowest. The WBI values of Si
Fe and Ge
Fe are lower than Pb
Fe, while that of Si
Ru is lower than Pb
Ru (see Figure 3). The findings may be explained on the basis of possible bonding interaction of ME---HM. The WBI values of ME---HM are 0.52 in I, 0.40 in II, 0.29 in III, 0.23 in IV, 0.37 in V, 0.27 in VI, 0.21 in VII, 0.19 in VIII, 0.19 in IX, 0.17 in X, 0.15 in XI, and 0.15 in XII. The results reveal that there is a reasonable bonding interaction of FeSi---HFe in I, FeGe---HFe in II, and RuSi---HRu in V. Thus, the existence of such a bonding interaction weakens the Fe
Si, Fe
Ge, and Ru
Si bonds as compared to the corresponding M
Pb bond. The calculated NPA charge distributions indicate that the metal atoms and the 3356

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Table 2. M
E Bond Distances and Bond Dissociation Energy (BDEs) of the M
E Bond in Metallo-ylene Complexes (kcal/mol) BDE complex

bond distance (Å) M
E

ionic fragments (singlet state)

neutral fragments (doublet state)

ref

[(η5-C5H5)(CO)3Cr-SiMe]

2.482

143.4

75.7

31

[(η5-C5H5)(CO)3Cr-GeMe]

2.615

151.6

76.2

30, 31

[(η5-C5H5)(CO)3Cr-SnMe] [(η5-C5H5)(CO)3Cr-PbMe]

2.811 2.918

141.1 133.5

63.8 51.3

31 31

[(η5-C5H5)(CO)3Mo-SiMe]

2.626

156.3

87.8

31

[(η5-C5H5)(CO)3Mo-GeMe]

2.695

153.3

83.2

30, 31

[(η5-C5H5)(CO)3Mo-SnMe]

2.909

142.1

71.3

31

[(η5-C5H5)(CO)3Mo-PbMe]

3.015

135.4

64.0

31

[(η5-C5H5)(CO)3W-SiMe]

2.628

160.2

100.0

[(η5-C5H5)(CO)3W-GeMe]

2.697

155.7

96.2

30, 31

[(η5-C5H5)(CO)3W-SnMe] [(η5-C5H5)(CO)3W-PbMe]

2.918 3.025

145.4 137.2

81.7 72.1

31 31

31

[(η5-C5H5)(Me3P)(H)2Fe-SiPh]

2.356

191.3

61.6

this work

[(η5-C5H5)(Me3P)(H)2Fe-GePh]

2.452

185.1

56.1

this work

[(η5-C5H5)(Me3P)(H)2Fe-SnPh]

2.590

175.5

47.8

this work

[(η5-C5H5)(Me3P)(H)2Fe-PbPh]

2.674

169.1

45.6

this work

[(η5-C5H5)(Me3P)(H)2Ru-SiPh]

2.428

185.4

67.0

this work

[(η5-C5H5)(Me3P)(H)2Ru-GePh]

2.503

179.3

61.6

this work

[(η5-C5H5)(Me3P)(H)2Ru-SnPh] [(η5-C5H5)(Me3P)(H)2Ru-PbPh]

2.667 2.759

173.1 165.3

56.6 53.1

this work this work

[(η5-C5H5)(Me3P)(H)2Os-SiPh]

2.402

186.5

67.9

this work

[(η5-C5H5)(Me3P)(H)2Os-GePh]

2.504

180.8

62.9

this work

[(η5-C5H5)(Me3P)(H)2Os-SnPh]

2.686

174.4

57.7

this work

[(η5-C5H5)(Me3P)(H)2Os-PbPh]

2.781

166.4

54.0

this work

C5H5 ligand always carry a negative charge, while the heavier group 14 elements (E) and EPh ligands are positively charged. The PMe3 ligands are positively charged. The hydride ligands are essentially neutral in character. 3.3. Energy Decomposition Analysis of the M
EPh Bonding of I
XII. In order to get more detailed insight into the nature of the M
EPh interactions, we carried out an energy decomposition analysis. The charges on the EPh ligands are positive, with values ranging from þ0.07 to þ0.35 (see Figure 3). For this reason, we have considered [(η5-C5H5)(Me3P)(H)2M]
and [EPh]þ fragments in the decomposition analysis. However, considering the smaller positive charge on EPh ligands, we have also carried out energy decomposition analysis on the neutral [(η5-C5H5)(Me3P)(H)2M] and [EPh] fragments. The results are given in Table 3, Table 4, and Figure 4. Table 2 shows the calculated bond dissociation energies of M
E bonds in metallo-ylene complexes of chromium, molybdenum, and tungsten30,31 and the complexes of the present study. Values of the dissociation energy of the M
E bond between ionic fragments [(η5-C5H5)(CO)3M]
and [EMe]þ (M = Cr, Mo, W) are smaller than those between ionic fragments [(η5-C5H5)(Me3P)(H)2M]
and [EPh]þ (M = Fe, Ru, Os). On the other hand, the reverse trend is found for dissociation energy between neutral fragments. We found that the M
E bond distances are relatively longer for metallo-ylene complexes of Cr, Mo, and W than those for Fe, Ru, and Os relative to the sum of the covalent radii of metal and E atoms.56 The results reveal that the M
E bonds are stronger in metallo-ylene complexes of

Fe, Ru, and Os than in the complexes of Cr, Mo, and W. Thus, the bonding between neutral fragments is a better bonding scheme than that between ionic fragments. Table 3 shows calculated energy terms for the interaction between charged fragments [(η5-C5H5)(Me3P)(H)2M]
and [EPh]þ. As seen in Table 3, the interaction energies ΔEint (
181.2 to
211.2 kcal/mol) as well as bond dissociation energies ΔE(
BDE) (
165.3 to
191.3 kcal/mol) for M
E bonds in metallo-ylene complexes I
XII are rather high. It should be emphasized that the calculated energy contribution ΔEπ gives only the out-of-plane π-component of the [(η5-C5H5)(Me3P)(H)2M]
f [EPh]þ π back-donation. This is because the molecules have Cs symmetry and, thus, the orbitals can have only a0 (σ) or a00 (π) symmetry. Thus, the energy contributions of the a0 (σ) orbitals come from the [(η5-C5H5)(Me3P)(H)2M]
f [EPh]þ σ back-donation but also from the in-plane [(η5-C5H5)(Me3P)(H)2M]
f [EPh]þ π back-donation. For molecules that have only Cs symmetry, it is not possible to separate the latter two interactions because both orbitals have a0 symmetry. Figure 4 depicts the variation in interaction energies and bond dissociation energies ΔE(
BDE) for compounds I
XII. The contributions of the electrostatic interaction terms ΔEelstat are larger in all metallo-ylene complexes (I
XII) than the covalent bonding ΔEorb term; the M
E bond in each case has a degree of covalent character of between 36% and 48%. Table 3 also gives the breakdown of the orbital interactions ΔEorb into σ-donation and π-back-donation components. It is important to note that the π-bonding contribution is, in all complexes, 3357

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141.9


185.1

11.4


50.1(26.1%)


123.5


175.5

13.9


31.9(20.5%)


109.5


169.1

13.2


25.7(19.0%)
185.4

14.1


51.5(23.2%)


170.7

273.1
250.4


199.5


179.3

16.3


35.0(18.9%)


150.5

234.7
244.9


195.6


173.1

16.3


26.3(16.7%)


131.4

216.2
247.9


189.4


165.3

15.9


22.7(16.4%)


115.6

198.8
241.7


181.2

Pb


186.5

24.7


34.0(15.5%)


185.3

268.5
260.4


211.2

Si


180.8

25.5


29.1(15.2%)


162.7

238.7
253.3


206.3

Ge


174.4

22.0


23.9(14.9%)


136.3

214.1
250.3


196.4

Sn


166.4

20.4


21.0(15.0%)


119.4

194.3
240.7


186.8

Pb

3358


56.1


47.8

24.0
45.6

20.6
67.0

22.4


256.4
35.6(12.2%)


61.6

16.5


206.
184.3
21.6(9.5%)


153.4

302.9


56.6

17.5


171.2
15.8(7.9%)


146.1

272.1


53.1

16.8


226.3
12.8(7.0%)


131.7

245.8


67.9

16.8


200.7
21.3(8.6%)


188.5

351.4


78.7


62.9

15.8


186.1
16.9(7.8%)


164.7

303.7


74.5


57.7

16.8


175.6
13.5(6.8%)


158.6

283.7


70.3 260.8


54.0

16.3


11.2(6.0%)


144.3

a Energy contributions in kcal/mol. b [(η5-C5H5)(Me3P)(H)2M] and [EPh] in the doublet state. c Values in parentheses are the percentage contribution to the total attractive interactions reflecting the covalent character of the bond. d Values in parentheses are the percentage contribution to the total orbital interactions, ΔEorb.

ΔE(
BDE)
61.6

23.2


168.0
15.9(8.6%)


180.9

386.5

29.2


189.7
21.9(10.3%)


125.7

243.4

ΔEprep


189.4
37.7(16.6%)


143.3

283.1


263.2
50.5(16.1%)


84.7

Pb


313.7(63.8%)
227.1(58.8%)
211.6(59.6%)
183.9(59.4%)
292.1(61.7%)
227.6(59.7%)
200.1(57.8%)
184.0(58.3%)
247.6(56.8%)
217.6(56.9%)
199.6(55.7%)
186.8(56.4%)


69.9

Sn

ΔEσ(a0 ) ΔEπ(a00 )d


74.1

Ge

ΔEorbc


78.1

Si


159.3


89.4

Pb


178.3


66.2

Sn

ΔEelstat


71.8

Ge

307.1


79.3

Si

401.2

Pb


90.8

Sn

M = Os

ΔEint

Ge

M = Ru

ΔEPauli

Si

M = Fe

Table 4. Energy Decomposition Analysisa of Metallo-ylidenes [(η5-C5H5)(Me3P)(H)2M
EPh] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb) at BP86/TZ2P using Neutral Fragmentsb

Energy contributions in kcal/mol. b Values in parentheses are the percentage contribution to the total attractive interactions reflecting the covalent character of the bond. c Values in parentheses are the percentage contribution to the total orbital interactions, ΔEorb.

a

13.6

ΔEprep

ΔE(
BDE)
191.3


168.1


63.6(27.4%)

ΔEπ(a00 )c

189.9
236.9


182.2

Sn


231.7(47.8%)
192.0(43.7%)
155.4(38.8%)
135.2(36.3%)
222.2(47.0%)
185.5(43.1%)
157.7(38.9%)
138.3(36.4%)
219.3(45.7%)
191.8(43.1%)
160.2(39.0%)
140.4(36.8%)

ΔEσ(a0 )

211.2
245.3


189.5

Ge

ΔEorbb

242.8
247.6


196.9

Si

280.1
253.3

Pb


204.9

Sn

M = Os

ΔEint

Ge

M = Ru

ΔEPauli ΔEelstat

Si

M = Fe

Table 3. Energy Decomposition Analysisa of Metallo-ylidenes [(η5-C5H5)(Me3P)(H)2M
EPh] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb) at P86/TZ2P

Organometallics ARTICLE

dx.doi.org/10.1021/om200252t |Organometallics 2011, 30, 3353–3361

Organometallics significantly smaller than the σ-bonding contribution (see Table 3). From the data presented in Table 2, it can be concluded that (i)

Figure 4. Trends of the absolute values of interaction energy ΔEint and ΔE(BDE) (in kcal/mol) for [(η5-C5H5)(Me3P)(H)2M]
and [EPh]þ fragments (singlet states) and [(η5-C5H5)(Me3P)(H)2M] and [EPh] fragments (doublet states) from silicon to lead in the metallo-ylenes [(η5-C5H5)(Me3P)(H)2M
EPh] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb).

ARTICLE

EPh ligands in these systems behave predominantly as σ donors; (ii) the interaction energy increases in the order Fe < Ru < Os; and (iii) the absolute values of the ΔEPauli, ΔEint, and ΔEelstat contributions to the M
E bonds decrease in the order Si > Ge > Sn > Pb. The EDA results of the interaction between neutral fragments [(η5-C5H5)(Me3P)(H)2M] and [EPh] (M = Fe, Ru, Os; E = Si, Ge, Sn, Pb) are given in Table 4. The data show that the interaction energies as well as bond dissociation energies between neutral fragments in metallo-ylene complexes I
XII are significantly smaller than those between ionic fragments [(η5C5H5)(Me3P)(H)2M]
and [EPh]þ (see Figure 4). Values of the Pauli repulsive terms, ΔEPauli, are significantly larger for interactions between neutral fragments than for interactions between charged fragments (Table 3). The interactions between neutral fragments show a strong σ bond and very weak π bond between the fragments. In contrast to the interaction between charged fragments, where the electrostatic interactions, ΔEelstat, are greater than the orbital interactions, ΔEorb, the orbital interactions, ΔEorb, are larger than the electrostatic interactions, ΔEelstat, for interactions between neutral fragments. In the case of homolytic bond dissociation, the M
E bond in each case has a degree of covalent character of between 56% and 64%.

Figure 5. Plot of some relevant molecular orbitals of [(η5-C5H5)(Me3P)(H)2Os
GePh], X. 3359

dx.doi.org/10.1021/om200252t |Organometallics 2011, 30, 3353–3361

Organometallics To visualize the significant M
Ge and M
H covalent interactions, envelope plots of relevant molecular orbitals for [(η5 -C 5 H 5 )(Me 3 P)(H)2 Os-GePh] X are given in Figure 5. Figure 5A (HOMO) is mainly the lone pair orbital at Ge, with some in-plane pseudo-π-bonding contributions. Figure 5B (HOMO
4) shows mainly the Os
Ge σ-bonding orbital, whereas Figure 5C depicts Os
Ge out-of-plane π bonding. Figure 5D gives a pictorial description of the Os
H bonds. The LUMO (Figure 5E) is a nonbonding π orbital.

4. CONCLUSIONS From the above-presented theoretical studies of the structure and bonding in 12 terminal metallo-ylenes of iron, ruthenium, and osmium, one can draw the following conclusions: 1. Here, for the first time, we reported the geometry and electronic structure, as well as analyzed the nature, of M
EPh bonds in the terminal metallo-ylenes of iron, ruthenium, and osmium [(η5-C5H5)(Me3P)(H)2M(EPh)] (where M = Fe, Ru, and Os, and E = Si, Ge, Sn, and Pb). 2. The M
E bonds in the studied complexes are essentially M
E single bonds. In all studied complexes, the π-bonding contribution to the total M
EPh bond is significantly smaller than that of the σ-bonding and increases upon going from M = Fe to Os. Thus, in the EPh ligands the E atom dominantly behaves as an σ donor. 3. The nature of the E of EPh has a significant effect on the M
P bonding: The M
P bond distances, bonds trans to EPh, decrease upon going from SiPh to PbPh. The variation in M
P bond distances may be due to the trans effect. 4. The contributions of the electrostatic interactions, ΔEelstat, to the M
EPh bonds are larger in all complexes I
XII than the covalent bonding, ΔEorb. In contrast to the interaction between charged fragments, where the electrostatic interactions, ΔEelstat, are greater that the orbital interactions, ΔEorb, the orbital interactions, ΔEorb, are larger than the electrostatic interactions, ΔEelstat, for interaction between neutral fragments. 5. Values of bond dissociation energy of the M
E bond between ionic fragments [(η5 -C 5 H 5 )(CO)3 M]
and [EMe]þ (M = Cr, Mo, W) are larger than those between ionic fragments [(η5-C5H5)(Me3P)(H)2M]
and [EPh]þ. On the other hand, the reverse trend is found for dissociation energy between neutral fragments. The M
E bond distances are relatively longer for metallo-ylene complexes of Cr, Mo, and W than those for Fe, Ru, and Os relative to sum of covalent radii of metal and E atoms.56 The results reveal that the M
E bonds are stronger in metallo-ylene complexes of Fe, Ru, and Os than in the complexes of Cr, Mo, and W. We believe that a more detailed understanding of the bonding in metallosilylene, metallogermylene, metallostannylene, and metalloplumbylene complexes is a requisite, particularly for the synthesis of terminal transition metallo-ylenes. In this respect, the above-presented findings are important contributions to the rapidly developing metallo-ylenes. ’ ASSOCIATED CONTENT

bS

Supporting Information. Cartesian coordinates of the optimized geometries of I
XII. This material is available free of charge via the Internet at http://pubs.acs.org.

ARTICLE

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

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