Structural, Theoretical and Spectroscopic Characterisation of a Series of Novel Gold(I)-Norbornene Complexes Supported by Phenanthrolines: Effects of the Supporting Ligand

A Journal of

Accepted Article

Title: Structural, theoretical and spectroscopic characterisation of

a series of novel gold(I)-norbornene complexes supported by

phenanthrolines: effects of the supporting ligand

Authors: Maria Agostina Cinellu, Massimiliano Arca, Fabrizio Ortu,

Sergio Stoccoro, Antonio Zucca, Anna Pintus, and Laura

Maiore

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content of this Accepted Article.

To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201901116

Link to VoR: http://dx.doi.org/10.1002/ejic.201901116

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

Structural, theoretical and spectroscopic characterisation of a series of novel

gold(I)-norbornene complexes supported by phenanthrolines: effects of the

supporting ligand

a,b

c

d,e

a,b

Maria A. Cinellu, Massimiliano Arca, Fabrizio Ortu, Sergio Stoccoro, Antonio Zucca,

c,*

a,*

Anna Pintus and Laura Maiore

a

Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Via Vienna 2, 07100 –

Sassari, Italy

b

Consorzio Interuniversitario Reattività Chimica e Catalisi (CIRCC), Bari, Italy

c

Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, S. S. 554 –

bivio per Sestu, 09042 – Monserrato, Italy

d

School of Chemistry, The University of Manchester, Oxford Road, M13 9PL – Manchester,

UK

e

School of Chemistry, University of Leicester, University Road, LE1 7RH – Leicester, UK

2

Abstract. A series of novel gold(I) alkene complexes of general formula [Au(N^N)(η -nb)][PF ]

6

[

N^N = PHEN (1,10-phenanthroline), NCP (2,9-dimethyl-1,10-phenanthroline), 4,7-DMP (4,7–

dimethyl-1,10-phenanthroline), TMP (3,4,7,8–tetramethyl-1,10-phenanthroline), BTP (4,7-

diphenyl-1,10-phenanthroline) and BTC (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline); nb =

norbornene] were synthesized by a novel synthetic pathway. The novel cationic gold(I)-

1

13

norbornene complexes were fully characterized by H and C NMR spectroscopy and the crystal

structure of three complexes was solved by single crystal X-ray diffraction. The correlations

between the nature and position of the substituents on the ancillary ligand and the spectroscopic

and structural data highlight variations on the nature of the bonding. The combination of

experimental and DFT data allowed to evaluate the extent of σ-donation and π back-donation in

the bond with the olefin, suggesting that a fine interplay between electronic and steric effects on

the ancillary ligand can affect the bond properties and structural features of the complexes.

Keywords. Gold-alkene compounds, back-bonding, DFT, NBO, N-ligands

1

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

Introduction

Gold-alkene complexes are known to play a key role as intermediates in the formation of carbon-

1

,2

3,4

5

heteroatom bonds,

such as hydroaminations

and hydroxylation, in catalyzed

6

7

hydrogenations, in oxidative cleavage of alkenes, and, as recently found, in Au-mediated

8

Negishi cross-coupling reactions. Therefore, these compounds have been the subject of

9

extensive studies and a variety of them were prepared and fully characterized.

1

0

11

The first alkene adducts of Au(I)-Cl were reported in the 1960s by Chalk and Hüttel. Such

species, together with others successively developed by Hüttel showed poor thermal and solution

9

stability. Since the end of the 1980s, a number of stable gold(I) alkene complexes were

9

,12

synthesized and fully characterized, in many cases also by crystal X-ray diffraction. Important

1

13

correlations between spectroscopic - mainly H and C NMR - and structural data could be

established, which in some cases were further supported by theoretical calculations, leading to

1

3,14

more detailed information on the nature of the gold-alkene bond.

Most of the reported

9

,10

gold(I)-alkene complexes are cationic 14- or 16-electron derivatives

and, apart from

homoleptic species, they are generally two-coordinate complexes supported by neutral or anionic

ancillary ligands, such as tertiary phosphines, heterocyclic NHC carbenes, or halides, while only

a few three-coordinate derivatives supported by chelating N^N ligands have been characterized.

1

5,16

By contrast, the first π-alkene gold(III) complexes appeared more recently in the literature,

1

5a,c

and only two of them were structurally characterized.

The picture that emerges from combined experimental data and theoretical analysis is that the

nature and strength of the gold-alkene bond is greatly influenced by the oxidation state of the

central metal ion, the nature of the ancillary ligand(s) and that of the alkene. In gold(I)

complexes π-back-donation was found to be highly tunable. Generally, in cationic two-

coordinated gold(I) complexes π-back-donation contribution in the gold-alkene bond is quite

1

7

+

small, while in three-coordinate complexes, such as those of the type [Au(N^N)(alkene)]

bearing chelating N^N ligands, its contribution is comparable to, if not as large as, the σ

1

3,14h

1

13

donation.

Indeed, a considerable upfield shift of the H and C resonances of the

coordinated olefin and significant lengthening of the C=C bond distance are generally observed

for these complexes. At variance, bonding in gold(III) derivatives relies almost entirely on the

1

13

alkene"Au σ-donation and, consistently, H resonances are downfield shifted, while

C

resonances are only slightly upfield shifted, accompanied by a modest elongation of the C=C

bond distance.

2

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

Some of the authors previously reported the study of uncommon oxygen transfer reactions from

R

a series of gold(III) oxo-bridged complexes of the type [Au (bipy ) (µ-O) ][PF ] [bipy = 6(6ꞌ)-

2

6 2

14h,18

alkyl-substituted 2,2ꞌ-bipyridines] to olefins,

leading to the isolation of a variety of very

R

2

stable cationic gold-alkene complexes [Au(bipy )(η -alkene)][PF ]. The formation of such

6

species occurred via reductive elimination from the corresponding gold(III) auraoxetane

R

2

intermediate [Au(bipy )(κ -O,C-2-oxyalkenyl)][PF ], as ascertained in the case of the reaction

6

1

8a

with norbornene, where this intermediate could be isolated and structurally characterized.

We have now shifted our attention towards gold(I) alkene complexes, owing to their potential

applications to catalysis. As a part of our investigations, we have prepared a series of novel

gold(I) 16-electrons alkene complexes with norbornene (nb), supported by variously substituted

2

1

,10-phenanthroline ligands (N^N), of general formula [Au(N^N)(η -nb)][PF ] with the aim to

6

gain further insight into the impact of the supporting ligand on the strength of the gold(I)-alkene

complexes. A simple, straightforward synthetic methodology was employed. As shown in the

literature for a series of gold(I) π-complexes supported by tertiary and chelating phosphines,

these derivatives can be similarly obtained by reaction of the proper precursor [Au(L)Cl], where

1

9

L is a chelating N^N ligand, with a silver salt and the desired olefin. All the complexes were

characterized by means of analytical and spectroscopic techniques and the molecular structures

of three of them were determined via single crystal X-ray diffraction studies. Additionally, the

nature of the gold(I)-alkene bond and the effect of the supporting ligand was studied also by

using Density Functional Theory (DFT) calculations, in order to elucidate the role of electronic

and steric effects in the bond properties and structural features of the complexes.

Results and Discussion

Synthesis and characterization

The hexafluorophosphate salts of the new three-coordinate gold(I) norbornene complex cations

2

+

[

Au(N^N)(η -nb)] [N^N = PHEN (1,10-phenanthroline) (1-PF ), NCP (2,9-dimethyl-1,10-

6

phenanthroline) (2-PF ), 4,7-DMP (4,7–dimethyl-1,10-phenanthroline) (3-PF ), TMP (3,4,7,8–

6

tetramethyl-1,10-phenanthroline) (4-PF ), BTP (4,7-diphenyl-1,10-phenanthroline) (5-PF ) and

6

BTC (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) (6-PF ); nb = norbornene] (Scheme 1)

6

were synthesized by a simple synthetic pathway.

3

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

2

Scheme 1. General structure of the nb complexes [Au(N^N)(η -nb)][PF ] (1-PF – 6-PF ) and of the N^N ligands.

6

2

Complex [Au(NCP)(η -nb)][PF ], 2-PF , was initially obtained by reaction of the dinuclear oxo-

6

2

0

bridged complex [Au(µ-O)(NCP)] [PF ] (AuoxoNCP) with excess norbornene in MeCN-H O

2

6 2

2

solvent mixture (Scheme 2, route A). As previously observed in the case of the analogous 6,(6ꞌ)-

1

8a

(di)substituted 2,2ꞌ-bipyridine derivatives,

a mixture of the gold(I) alkene complex

2

[

Au(NCP)(η -nb)][PF ] (2-PF ) and its gold(III) precursor, the auraoxetane [Au(κ -O,C-2-

6

oxynorbornyl)(NCP)]PF ] (2O-PF , data for this compound are reported in ESI), was obtained.

6

Although the molar ratio of the two complexes can be optimized to obtain the olefin complex 2-

PF as the major product by varying the concentration of the reagents, separation of the target

6

compound from the mixture required further workup (see ESI). Moreover, this method could be

applied only to the 2,9-dimethyl-1,10-phenanthroline, the latter being the only ligand capable of

III

stabilizing the Au oxo complex. A more effective synthetic route towards the target complexes

was developed, that could also be applied to all the phenanthroline derivatives under study

(

Scheme 1). According to this method, complex 2-PF was obtained in higher yields, and as the

6

only product, by reacting the gold(I) adduct [AuCl(NCP)] with an equimolar amount of nb in the

presence of AgPF , as depicted in Scheme 2 (route B). The chloride precursor [AuCl(NCP)] (2a-

6

Cl) was easily obtained by reaction of NCP with an equimolar amount of [AuCl(THT)] in

CH Cl . Abstraction of the chloride with AgPF and subsequent reaction with nb afforded the

2

6

target compound 2-PF as the only product and in a very short reaction time (about ten to forty

6

minutes for the whole procedure). Complexes [AuCl(N^N)] with ligands N^N = PHEN, 4,7-

DMP, TMP, BTP and BTC are unstable in solution and when exposed to light. Nevertheless,

complexes 1-PF , 3-PF – 6-PF could be obtained following one-pot procedures by mixing the

6

ligand N^N and [AuCl(THT)] in CH Cl , followed by addition of AgPF and nb; the resulting

2

6

norbornene complexes were isolated as reported for 2-PF (see Experimental for further details).

6

Attempts to obtain analogous complexes with 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline

disulfonic acid disodium salt were not successful and led to the deposition of metallic gold as the

4

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

reagents were mixed, both at room temperature and in an ice bath.

Scheme 2. Syntesis of complexes 1-PF – 6-PF according to routes A and B.

6

Complexes 1-PF – 6-PF are soluble in organic solvents (CHCl , CH Cl , CH CN and

6

3

2

3

1

CH COCH ), and they are stable in the solid state. The H NMR spectrum of 2-PF in CD Cl

2

3

6

2

solution (Figure 2, a) shows all the resonances of the NCP ligand shifted to higher frequencies,

H4ꞌ being the most deshielded proton with respect to the uncoordinated ligand, with a

coordination-induced shift ∆δ(H) [∆δ(H) = δ(H)_f_r_e_e− δ(H)_c_o_o_r_d] of –0.66 ppm (see Figure 1 for

the NMR numbering scheme). Additionally, also the methyl protons are deshielded as compared

14h,18

to the starting material. As previously observed for most gold(I)-alkene complexes,

the

olefin protons are significantly shifted to high field with respect to those of the free alkene, with

a ∆δ(H) of 1.70 ppm; also the H7_s_y_n(∆δ = 0.22 ppm) and the H1,4 resonances (∆δ = 0.43 ppm)

are shifted to high field, while the other aliphatic protons resonate at lower field or remain almost

unchanged (H7 ). In a similar fashion, the resonances of the olefin C=C carbon atoms and of

anti

the bridgehead C7 are likewise shifted upfield, with coordination-induced shifts ∆δ(C) [∆δ(C) =

δ(C) −δ(C)_c_o_o_r_d] of 53.33 and 5.39 ppm, respectively (Figure 2, b). The opposite trend was

free

instead observed for the other aliphatic carbons of nb, which are only slightly downfield-shifted

(∆δ(C) range –1.16 - –1.22 ppm). Assignments of nb and NCP carbon atoms in complex 2-PF₆

were accomplished by NOESY (Figure S2, a) and HSQC experiments (Figure S2, b).

An in-depth NMR characterization was also carried out for complexes 1-PF and 3-PF – 6-PF ,

6

1

13

1

(

H and C{ H} spectra of the complexes are shown in the Supporting Information, Figures S3-

1

2

S12). As previously observed, the olefin proton and carbon chemical shifts are the most

affected by π-back-donation contribution, and high field coordination shift increases on

increasing the extent of such contribution. Within this set of phenanthroline complexes, the

5

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

nature and position of the substituents on the phenanthroline scaffold, in addition to affecting the

electronic and steric properties of the ligand, are expected to induce differences to the chemical

shifts of the olefin proton and carbon atoms. Indeed, in all complexes the olefin protons resonate

at high fields with respect to the free nb, and significant differences in ∆δ(H) values are

observed, depending on the supporting ligand. Complex 1-PF , bearing the unsubstituted PHEN

6

ligand, features ∆δ(H) of 1.60 ppm, introduction of the electron-donating methyl groups on the

phenanthroline scaffold results in increased ∆δ(H) values from 1.69 ppm in 6-PF to 1.73 ppm in

6

4

-PF (see Table 1), while the presence of phenyl substituents, on increasing charge

6

delocalization, has the effect to reduce ∆δ(H), that in complex 5-PF is of 1.60 ppm. The small

6

∆

δ(H) difference observed between 2-PF and 3-PF , both bearing dimethyl substituted

6 6

phenanthrolines, may be ascribed to steric effects.

Small but significant differences were found also in the ∆δ(C) values of the olefin carbons, as a

result of combined electronic and steric properties of the supporting ligands. In all complexes the

resonance of the olefin carbons are shifted to high fields: complex 1-PF , bearing the

6

unsubstituted PHEN, shows a ∆δ(C) value of 51.88 ppm, complexes 2-PF , 3-PF and 4-PF ,

6

bearing only methyl substituents on the phenanthroline scaffold, show ∆δ(C) values of, 53.33,

4.56 and 53.55 ppm, respectively, while the presence of phenyl substituents in complexes 5-PF₆

5

and 6-PF results in slightly lower ∆δ(C) values (52.36 and 51.86 ppm, respectively). Steric

6

effects on the ∆δ(C) values are more evident than for the ∆δ(H) ones. It is worth mentioning that

the ∆δ(C) values of the olefin carbons in 1-PF – 6-PF are significantly larger than those of di-

6

1

7,22

coordinated gold(I) complex cations with norbornene previously reported in the literature.

A trend was also identified for the chemical shift of the H7_s_y_nand C7 of norbornene, being both

sensitive to the electronic and, to a larger extent, the steric features of the co-ligand. Indeed,

complexes 2-PF and 6-PF , bearing methyl substituents in 2,9 position, showed the H7

syn

6

resonance at 0.87 and 0.90 ppm, respectively, with the lowest ∆δ(H) values (0.22 and 0.19 ppm,

respectively). On the other hand, complexes 1-PF and 3-PF , with no methyl substituents near

6

the coordination sites of the phenanthroline, featured ∆δ(H) values of 0.28 and 0.29,

respectively. Electronic effects seem to be dominant in the case of the tetra-methyl substituted

TMP complex 4-PF which shows the maximum ∆δ(H) value of 0.30 ppm. Likewise, but to a

6

lesser extent, the resonances of the C-7 atom are shifted to high field for all the complexes, with

∆

δ(C) values in the range 4.87 (1-PF ) – 6.90 (6-PF ) ppm.

6 6

Overall, the trend shown by the NMR data is in line with that observed for the structural

parameters determined for complexes 1-PF , 2-PF , and 6-PF .

6

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

2

+

Figure 1. Numbering scheme for the [Au(N^N)(η -nb)] scaffold in complexes 1-PF – 6-PF .

6

Table 1. Chemical shifts of selected proton and carbon resonances. ∆δ(H) [∆δ(H) = δ(H) − δ(H)_c_o_o_r_d] and ∆δ(C)

free

ov

[

∆δ(C) = δ(C)_f_r_e_e− δ(C)_c_o_o_r_d] are reported in parenthesis; = overlapped

1

13

H (CD Cl )

C (CD CN)

3

2

HC=CH

CH H-7

CHH_a_n_t_i-7

HC=CH

C7

syn

nb

6.00

1.09

1.30

135.90

49.10

ov

1

2

3

4

5

6

-PF₆

4.40 (1.60)

4.30 (1.70)

4.29 (1.71)

4.27 (1.73)

4.40 (1.60)

4.31 (1.69)

0.81 (0.28)

0.87 (0.22)

0.80 (0.29)

0.79 (0.30)

0.85 (0.24)

0.90 (0.19)

1.25

84.02 (51.88)

82.57 (53.33)

81.34 (54.56)

82.35 (53.55)

83.54 (52.36)

84.04 (51.86)

44.23 (4.87)

43.71 (5.39)

42.50 (6.60)

43.84 (5.26)

44.04 (5.06)

42.20 (6.90)

ov

1.29

ov

1.24

ov

1.23

ov

1.28

ov

1.32

7

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

a)

HC=CH

H7_a_n_t_i

H7_s_y_n

b)

HC=CH

C7

1

13

Figure 2. a) H (CD Cl ) and b) C (CD CN) NMR spectra of 2-PF at 298 K.

2

3

6

Structural characterization

X-ray quality crystals of 1-PF , 2-PF and 6-PF were obtained by slow diffusion of diethyl ether into a

6

dichloromethane solution, and their molecular structures were determined via single crystal X-ray

diffraction (XRD) studies (Figure 3 and Table 2). 2-PF crystallises in the monoclinic I2/a, whilst 1-PF

6

8

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

and 6-PF crystallise in the orthorhombic Pnma and P2 2 2 , respectively. All the complexes display

6

1 1 1

2

three-coordinate Au centers, the C=C system of the norbornene η -coordinating ligand lying roughly on

the same plane of the Au(N^N) fragment [2-PF : Au(1)–C(15) 2.116(4) Å, Au(1)–C(16) 2.120(6) Å; 1-

6

PF : Au(1)–C(13) 2.130(10), Au(1)–C(13)i 2.130(10); 6-PF : Au(1)–C(27) 2.099(12) Å, Au(1)–C(28)

6

2

.108(10) Å; 2-PF : C(15)–Au(1)–C(16) 38.8(2)°; 1-PF : C(13)–Au(1)–C(13)i 39.7(4)°; 6-PF : C(27)–

6 6 6

Au(1)–C(28) 39.3(5)°] (i = +x, ½–y, +z). The phenanthroline ligands act as bidentate donors [2-PF₆:

N(1)–Au(1)–N(2) 75.39(19)°; 1-PF : N(1)–Au(1)–N(1)i 76.2(4)°; 6-PF : N(1)–Au(1)–N(2) 75.1(3)°; 2-

6

PF : Au(1)–N(1) 2.218(4) Å, Au(1)–N(2) 2.231(6) Å; 1-PF : Au(1)–N(1) 2.205(8), Au(1)–

6

N(1)i 2.205(8); 6-PF : Au(1)–N(1) 2.196(8) Å, Au(1)–N(2) 2.186(8) Å].

6

The C=C distances of the norbornene ligands in 2-PF and 6-PF [1.408(7) Å and 1.415(16) Å

6

2

1

respectively] are elongated with respect to the free alkene, in agreement with π back-donation

from the metal center. Interestingly, this lengthening is more marked compared to those observed

1

7,22

in the structures of other cationic gold(I) complexes with norbornene,

in agreement with the

NMR data discussed above. On the other hand, in the case of 1-PF rigorous statistical

6

comparisons could not be drawn due to the large uncertainty on the metric parameters [1.45(2)

Å].

The solid-state structure of 2-PF propagates via a combination of π-stacking and Au···π(arene)

6

interactions. The distance between the phenanthroline scaffolds is 3.638(5) Å, with the two

neighbouring units positioned in a perfectly parallel arrangement [phenanthroline twist angle

0

.0(6)°]. The proximity of the two molecules of complex in the solid state establishes also

secondary inter-molecular semi-localised Au···π(arene) interactions between the ligands and the

i

metal centers [Au(1)···C(6) 3.566(7) Å, Au(1)···C(7) 3.620(7) Å] ( = ½–x,+y, 1–z), as

2

3

previously observed in gold(III) phenanthroline complexes only. π-stacking and Au···π(arene)

interactions can also be observed in the case of 1-PF , with shorter phenanthroline-

6

phenanthroline distances compared to 2-PF [3.350(2) Å; phenanthroline twist angle 1.2(3)°] and

6

similar long range Au···phen contacts [3.596(8) Å] to those observed for 2-PF . In the case of 6-

6

PF packing analysis is unremarkable and no significant long-range interactions are observed.

6

9

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

Figure 3. Molecular structures of 1-PF , 2-PF and 6-PF with ellipsoids set at 50% probability level; hydrogen

6

atoms have been omitted for clarity.

Table 2. Selected bond lengths (Å) and angles (º) in 1-PF , 2-PF and 6-PF

6

1

-PF₆

2-PF₆

6-PF₆

2

.218(4)

.231(6)

2.196(8)

2.186(8)

Au−N_p_h_e_n

Au−C_n_b

2.205(8)

2

.116(4)

.120(6)

2.099(12)

2.108(10)

2.130(10)

Au···nb

2.004(9)

1.45(2)

76.2(4)

1.997(4)

1.408(7)

75.39(19)

1.981(8)

1.415(16)

75.1(3)

C=C_n_b

N1−Au1−N2

1

21.96(16)

23.8(2)

123.2(4)

122.2(4)

N−Au−C_n_b

C −Au−C

121.6(4)

39.7(6)

38.8(2)

39.3(5)

nb

Theoretical calculations

2

4

Density functional theory (DFT)

level calculations represent an invaluable tool in

understanding the electronic structure of metal complexes, and they have been extensively

1

0

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

exploited to investigate structure/property relationships in a large variety of compounds at an

acceptable computational cost. In order to select an appropriate computational setup, preliminary

+

calculations were performed on complex 1 with different combinations of functionals and basis

sets (BSs). Following the results reported by some of the authors on related metal

14h,25,26,27

28

29

complexes,

the well-known hybrid mPW1PW and PBE0 (PBE1PBE) functionals

3

0

were tested, along with the long-range corrected LC-wPBE functional, in order to verify the

3

1

influence of London dispersion effects on the optimized geometries. Ahlrichs pVDZ basis sets,

including polarization functions, were employed for the organic framework, while for the heavier

3

2

gold species two different BSs with Relativistic Effective Core Potentials (RECPs) were

3

34

evaluated, namely LANL08(f) and CRENBL. A comparison between the bond distances and

+

angles determined by single crystal XRD for 1 and the corresponding optimized parameters

indicated PBE0/LANL08(f) as the combination of BS and functional reproducing most

accurately the experimental geometry. In particular, the sum of the squared errors between the

various sets of data was considered (Table S2 in the ESI). This setup was therefore adopted to

optimize the geometry of the N^N ligands (N^N = PHEN, NCP, 4,7-DMP, TMP, BTP, BTC,

+

Scheme 1), free norbornene (nb), and the complex cations 1 – 6 in the gas phase. A very good

3

5

agreement was found between the optimized and structural data, the bond lengths and angles

differing by less than 0.03 Å and 3°, respectively, with the exception of the torsion angles

between the phenyl substituents and the plane of the phenanthroline backbone in BTP and BTC,

which were overestimated by about 3–9° (Figure 4 and Tables S3-S4 in the ESI). An

examination of the highest occupied Kohn–Sham (KS) molecular orbitals (MOs) calculated for

the free N^N ligands shows the KS-HOMO-1 and KS-HOMO-3 MOs are built up of the out-of-

phase and in-phase combinations, respectively, of the nitrogen lone pairs (LPs) available for σ-

coordination to the metal ion (Figure 5 for KS-HOMO-1 MOs). In the case of norbornene, the

KS-HOMO is a π-in-nature bonding MO localized on the C2-C3 bond and available for metal σ-

*

donation, while the KS-LUMO is the corresponding π antibonding MO (Figure 5, bottom),

involved in π back-bonding (see below).

+

In the optimized structures of complexes 1 – 6 (Figure 6 and Table 3), the gold atom shows a

pseudo-planar coordination (C19-N1-Au-C2 and C17-N2-Au-C3 dihedral angles in the range

1

76.00-178.35°; Figure 6), with N-Au-N bite angles of about 75° (experimental N1-Au-N2 angle

+

=

76.2(4), 75.39(19), and 75.1(3) ° for 1 , 2 , and 6 , respectively; Table 2).

3

6

Average N–Au distances were calculated in the range 2.208-2.227 Å, corresponding to Wiberg

bond indices of 0.282-0.294 (Table S5 in the ESI), in agreement with the structural data, where

1

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

the corresponding bond lengths are identical within error. As for the norbornene, as expected

2

and in agreement with the experimental NMR and structural data, the η -coordination to the

metal results in a lengthening of the C2-C3 bond by about 0.08 Å in the complexes with respect

to the free ligand. A modification in the positions of H2 and H3 leading to a change in the C6-

C1-C2-H1 and C5-C4-C3-H2 dihedral angles of about 30° was calculated. In parallel, a partial

pyramidalization of the C2 and C3 carbon atoms occurs (Au-C2/C3-H1/H2 angle = 109.56°).

Au–C bond lengths were found to be in the range 2.105-2.114 Å (Wiberg bond indices: 0.469-

0

.481), and the C2-Au-C3 angle amounts to about 39°.

A natural population analysis was carried out to evaluate the charge distribution within the

investigated systems (Table S5 in the ESI). In all complexes, the gold cation features a natural

electron configuration amounting to 10.3 |e|, in perfect agreement with the +I formal oxidation

state. The σ-coordination of the diamine to gold results in a decrease of about 0.08 |e| in the

negative charge calculated on the nitrogen atoms with respect to the free ligands [NPA charge on

N1 and N2: –0.449 (PHEN), –0.469 (NCP), –0.455 (4,7-DMP), –0.474 (TMP), –0.450 (BTP),

and –0.469 |e| (BTC)]. On the other hand, the C2 and C3 atoms of norbornene are more

+

negatively charged by about 0.1 |e| in 1 – 6 with respect to the free ligand (–0.225 |e|), due to

the π-back-donation experimented by the olefin in the complexes.

The natural population analysis was also exploited to investigate the bonding features of the

complexes in terms of second order perturbation theory (SOPT) of the Fock Matrix in the NBO

basis, showing that the N→Au interactions between the lone pairs (LPs) localized on the

+

phenanthroline N-atoms and the unoccupied natural orbitals of Au amount to 143.84 (1 ), 148.16

+

-1

+

(

2 ), 148.88 (3 ), 153.03 (4 ), 151.38 (5 ), and 154.58 kcal·mol (6 ). An increase in the energy

+

of this interaction is observed on passing from 1 , featuring unsubstituted phenanthroline as the

+

diimine ligand, to the complexes featuring disubstituted (2 , 3 , 5 ) and tetrasubstituted (4 and

+

6

) diimines, which is also reflected in a shortening of the Au-N bond lengths and an increase of

the Wiberg bond indices.

1

4h,37

According to the Dewar-Chatt-Duncanson bond model,

the bonding of norbornene to gold

can be partitioned in a σ-interaction (from the filled π-HOMO of norbornene to an empty AO

*

centered on the gold atom) and a 5d→π back-donation (from a filled 5d orbital of the metal to

the unoccupied antibonding π* orbital of the olefin).

+

In order to evaluate these contributions, the interaction between norbornene and the [Au(phen)]

3

8

+

cation was considered in terms of a Fragment Molecular Orbital (FMO) approach, applied to 1

1

2

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

as a model system (Figure 7). The KS-HOMO of norbornene (see below) is symmetry allowed to

+

σ-interact with the KS-LUMO of the [Au(phen)] cation, which is centered on the metal ion and

+

is mainly 6p in nature, resulting in the HOMO-2 and LUMO+6 MOs in 1 . The π back-bonding

y

+

occurs between the KS-LUMO of norbornene and the HOMO of [Au(phen)] , which features a

+

very large contribution from the 5d Au atomic orbital, to give HOMO-1 and LUMO+3 in 1 .

xy

CT

σ

+

NBO calculations show that the energy E of the nb→[Au(phen)] σ-interaction depends on the

–

1

nature of the N^N ligand and falls in the range 219.94-237.39 kcal·mol , while the π back-

CT

π

–1

donation E

is in the range 66.43-68.55 kcal·mol for all complexes (Table 4), thus roughly

1

7a

confirming the ratio of ~ 3 : 1 of forward to back-bonding calculated by Frenking and

+

13f

coworkers for the model fragment [Au(C H )] . The nature of these data show that while the

2

4

entity of the π back-donation is very similar for all of the complexes, the σ-donation is slightly

+

weaker for the N^N ligands featuring substituents at the 2- and 9- positions (i.e. in complexes 2 ,

+

4

, and 6 ), possibly due to their steric hindrance.

1

3

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

Figure 4. Molecular drawing and atom labelling scheme for the free ligands at the optimized geometry. Hydrogen

atoms were omitted for clarity in the case of phenanthroline derivatives.

Figure 5. Isosurface drawings of selected frontier Kohn–Sham molecular orbitals calculated for the free ligands at

the optimized geometry. Hydrogen atoms were omitted for clarity in the case of phenanthroline ligands. Cutoff

value = 0.05 |e|.

1

4

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

+

Figure 6. Molecular drawing and atom labelling scheme for complex molecules 1 – 6 at the optimized geometry.

Hydrogen atoms on the phenanthroline ligands were omitted for clarity.

Table 3. Selected optimized (Opt.) and available structural (Struct.) average bond lengths (Å) and angles (°) for

+

complex molecules 1 – 6 (numbering scheme as in Figure 6).

+

1

+

3

+

4

+

5

+

6

2

Struct.

Opt.

Struct.

Opt.

Struct.

Opt.

Au-N1

Au-N2

Au-C2

Au-C3

N1-C8

2.205

2.130

1.312

2.224

2.110

1.324

2.218

2.231

2.116

2.120

1.326

2.227

2.114

1.332

2.214

2.107

1.323

2.217

2.111

1.331

2.208

2.105

1.325

2.186

2.196

2.108

2.099

1.325

2.213

2.110

1.332

1

5

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

N1-C19

1.369

1.350

1.324

1.350

1.440

1.426

1.519

1.534

1.096

1.103

1.100

/

1.361

1.353

1.332

1.353

1.441

1.425

1.519

1.534

1.096

1.103

1.100

1.478

1.492

/

1.352

1.323

1.352

1.442

1.427

1.519

1.534

1.096

1.103

1.100

/

1.354

1.331

1.354

1.444

1.426

1.519

1.534

1.096

1.103

1.100

1.493

1.494

/

1.351

1.325

1.351

1.443

1.428

1.519

1.534

1.096

1.103

1.100

/

1.354

1.332

1.354

1.445

1.426

1.520

1.534

1.096

1.103

1.100

/

N2-C17

1.312

1.333

1.351

N2-C18

1.369

1.367

1.365

C18-C19

1.430

1.642

1.451

C2-C3

1.446

1.408

1.415

C1-C2

1.525

1.523

1.512

C3-C4

1.525

1.527

1.496

C1-C7

1.542

1.526

1.513

C4-C7

1.542

1.524

1.532

C2-H1

/

C3-H2

/

C7-H3

/

C7-H4

/

C8-C20

/

1.493

/

C17-C21

/

1.493

/

C10-C22

/

1.494

/

C15-C23

/

C10-C20

/

1.478

/

1.483

1.487

1.508

1.513

75.15

122.16

123.20

39.31

/

1.479

1.494

75.24

122.59

39.51

122.86

113.85

122.66

178.93

73.13

175.89

59.67

84.19

176.00

147.44

C15-C26

/

C8-C32

/

C17-C33

/

N1-Au-N2

N1-Au-C2

N2-Au-C3

C2-Au-C3

H1-C2-C3

H2-C3-C2

C1-C7-H3

C1-C7-H4

C8-N1-C19-C18

C17-N2-C18-C19

C6-C1-C2-H1

C5-C4-C3-H2

C6-C1-C7-H3

C6-C1-C7-H4

N1-Au-C2-C1

N2-Au-C3-C4

C19-N1-Au-C2

C17-N2-Au-C3

C6-C1-C2-Au

76.22

74.92

122.76

39.51

123.17

113.89

112.63

179.99

74.13

175.98

59.72

83.74

177.82

147.43

75.39

75.50

122.52

39.40

122.92

113.87

112.65

179.76

73.52

175.91

59.70

83.67

178.22

147.51

74.69

122.84

39.58

123.14

113.88

112.63

179.99

73.92

175.98

59.69

83.81

177.79

147.38

75.26

122.61

39.48

122.87

113.86

112.65

179.73

73.24

175.90

59.67

83.71

178.35

147.46

74.69

122.8

39.65

123.13

113.87

112.63

178.91

73.72

175.98

59.68

83.86

177.05

147.34

121.63

121.92

121.63

123.80

39.67

38.84

/

179.11

/

179.04

178.96

/

179.25

179.78

/

88.61

162.70

148.01

85.65

81.56

171.98

170.74

148.75

88.35

82.37

176.04

175.26

147.19

1

6

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

C5-C4-C3-Au

148.01

147.43

146.77

147.51

147.38

147.46

147.34

43.21

50.26

149.76

42.77

45.05

46.01

47.69

147.44

43.22

51.19

Au-C2-C1-C7

43.35

43.33

44.51

43.32

43.27

43.25

Au-C3-C4-C7

43.35

43.33

42.61

43.32

43.27

43.25

C9-C10-C20-C21

C16-C15-C26-C31

/

+

2

Figure 7. MO correlation diagram showing the interaction between the [Au(phen)] complex cation and η -

+

norbornene moieties in the complex molecule 1 , calculated at DFT level. The KS-HOMO, LUMO, LUMO+1,

LUMO+2, and LUMO+4, are centered on the PHEN ligand. Hydrogen atoms were omitted for clarity. Cutoff value

=

0.05 |e|.

-1

CT

Table 4. CT-SOPT energies (kcal∙mol ) calculated for the σ-donation (E _σ) from norbornene to the gold metal ion

CT

and the π back-donation (E _π) occurring from gold to the olefin, and energy difference ∆E_σ₋_πbetween the two

contributions.

+

1

2

3

4

5

6

CT

E

233.27

66.43

219.94

66.57

235.55

67.65

222.32

67.80

237.39

68.55

222.88

68.25

σ

CT

E

π

1

7

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

∆

E_σ₋_π

166.84

167.90

153.37

154.52

168.84

154.62

Conclusions

Six novel gold(I)-norbornene complexes supported by variously substituted phenanthroline

ligands were synthesized following a novel one-pot procedure requiring short reaction time and

affording 30 to 80% yields. The crystal structures of three of these complexes were solved by

single crystal X-ray diffraction analysis, confirming the pseudo-planar coordination geometry

around the metal centers. Theoretical calculations confirmed the bonding features hypothesized

for this class of compounds, and further elucidated the nature of the molecular orbitals involved.

1

13

Structural and H- and C-NMR data suggest that the nature of the substituent at the

phenanthroline ligands can finely tune the entity of the π back-donation. Furthermore, theoretical

calculations indicate that for all complexes the extent of σ-donation overcomes that of π back-

I

donation and that major differences occur in the former contribution to the bond between Au

and the olefin. It is worth noting that the position of the substituent rather than their aliphatic or

aromatic nature affects the entity of the σ-donation electron transfer. These findings suggest that

a fine interplay between electronic and steric effects on the ancillary ligand is responsible for the

overall bonding properties of the complexes, and the extension of the library of complexes

belonging to the title class of compounds might allow for a further elucidation of these aspects.

Experimental Section

Materials and methods. Reagents were used as received from commercial sources. Solvents were

dried prior to use by standard methods. [AuCl(THT)] was synthetized according to a literature

3

9

20

method. Compound AuoxoNCP was prepared according to a previously reported method.

The infrared spectrum of [AuCl(NCP)] was recorded with a Jasco FTIR 480 Plus

–

1

spectrophotometer in Nujol mulls (600 - 250 cm ), while KBr pellets were used for complex 2-

–

1

13

31

PF in the frequency range 4000-600 cm . H, C, P, HSQC and NOESY NMR spectra were

6

recorded at room temperature (298 K) with a Bruker Avance III 400 spectrometer operating at

4

00.1 and 100.6 MHz, respectively. Chemical shifts are given in ppm. Assignments of nb and

Me phen carbon atoms in complex 2-PF have been accomplished by HSQC and NOESY

2

6

experiments. Theoretical calculations were carried out on the nitrogen donors N^N (N^N =

PHEN, NCP, 4,7-DMP, TMP, BTP, BTC, Scheme 1), on norbornene (nb), on the cationic

+

[

Au(N^N)(nb)] metal complexes 1 – 6 , and on the [Au(PHEN)] complex fragment. All

1

8

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

4

0

calculations were carried out at the Density Functional Theory (DFT) level with the Gaussian

4

1

6 commercial suite of programs. After a set of preliminary calculations aimed at selecting the

2

9

most appropriate computational setup (see discussion above), the PBE0 hybrid functional was

3

1

adopted. Ahlrichs pVDZ basis sets (BSs) were employed for C, N, and H. For the heavier gold

species, the triple-zeta BSs in the revision by Roy et al., particularly re-contracted for DFT

4

2

calculations, supplemented by the polarization function proposed by Frenking, were chosen,

3

2

and Relativistic Effective Core Potentials (RECPs) were employed in order to account for

4

3

relativistic effects (LANL08(f)). BS data were extracted from the EMSL BS Library. The

molecular geometry optimizations were performed starting from structural data, when available.

Harmonic frequency calculations were carried out to verify the nature of the minima of each

4

36

optimized geometry. Natural atomic charges and Wiberg bond indices were calculated at the

4

5

optimized geometries at the same level of theory. The programs GaussView 6.0.16, Molden

4

6

47

5

.7, and Chemissian 4.53 were used to investigate the optimized structures and molecular

orbital shapes. The crystal data for complexes 1-PF , 2-PF , and 6-PF are compiled in Table S1.

6

Crystals of 1-PF and 6-PF were examined using a Bruker Apex II diffractometer with a CCD

6

area detector and a graphite-monochromated Cu Kα radiation (λ = 1.54178 Å). Crystals of 2-PF₆

were examined using an Oxford Diffraction diffractometer with a CCD area detector and a

mirror-monochromated Mo Kα radiation (λ = 0.71073 Å). Intensities were integrated from data

recorded on 1° (1-PF , 2-PF ) and 1.5° (6-PF ) frames by ω or φ rotation. Cell parameters were

6

refined from the observed positions of all strong reflections in each data set. Multi-scan

4

8

absorption correction with a beam profile was applied. The structures were solved using

4

9

2

50

SHELXS; the datasets were refined by full-matrix least-squares on all unique F values, with

anisotropic displacement parameters for all non-hydrogen atoms, and with constrained riding

hydrogen geometries; U (H) was set at 1.2 (1.5 for methyl groups) times U of the parent atom.

iso

eq

The largest features in final difference syntheses were close to heavy atoms and were of no

5

11

49,50

chemical significance. CrysAlisPro was used for control and integration, and SHELX

was

5

2

53

54

employed through OLEX2 for structure solution and refinement. ORTEP-3 and POV-Ray

were employed for molecular graphics. CCDC 1901009–1901011 contain the supplementary

crystal data for this article. These data can be obtained free of charge from the Cambridge

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Syntheses of [Au(NCP)(nb)][PF ] (2-PF ): Method A: to a stirred solution of compound

6

AuoxoNCP (452.7 mg, 0.4 mmol) in MeCN-H O (100 and 2.5 mL, respectively) was added nb

2

1

9

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

(1.24 g, 13.1 mmol) and the resulting solution stirred at room temperature for 15 days, with

exclusion of light. Afterwards, some metallic gold was separated by filtration through Celite, and

the solution evaporated to dryness. The crude product was extracted with diethyl ether (3 x 15

mL) to remove oxygenated norbornene derivatives and recrystallized from

dichloromethane/diethyl ether to afford a mixture of 2-PF (37% yield) and 2O-PF (29% yield)

6

1

(

H NMR criterium) as a pale yellow solid. A pure sample of 2-PF was obtained on addition of

6

MeOH to a dichloromethane solution of the mixture at –20 °C. X-ray quality crystals were

obtained as colourless needles from slow diffusion of diethyl ether into a dichloromethane

solution. Method B: to a stirred solution of NCP (217.6 mg, 1.0 mmol) in 20 mL of CH Cl was

2

added a solution of [AuCl(THT)] (317.3 mg, 1.0 mmol) in the same solvent and the resulting

mixture stirred at room temperature for 10 to 40 minutes, with exclusion of light. After filtration

over Celite to separate metallic gold, the solution was concentrated to a small volume; addition

of diethyl ether afforded [AuCl(NCP)], 2a-Cl, as a yellow solid (320.6 mg, 73%); m.p. 152 °C.

-1

Selected IR bands (ν/cm ; KBr pellet): 545 ν(Au-N), 332 ν(Au-Cl). The compound is unstable

in solution and light sensitive. Complex 2-PF was obtained by addition of nb (30.1 mg, 0.32

6

mmol) to an acetone suspension of 2a-Cl (141.1 mg, 0.32 mmol, 40 mL) followed by addition of

AgPF (81.9 mg, 0.32 mmol) to the resulting solution. The resulting suspension was stirred for

6

1

0 minutes and then filtered through Celite to separate AgCl; the filtered solution was

concentrated to a small volume and diethyl ether added to give 2-PF as a white solid: yield 82%.

6

Complexes 1-PF and 3-PF – 6-PF were obtained according to the same procedure but the

6

chlorido precursors were not isolated due to their instability in solution and when exposed to

light.

Analytical and spectroscopic data of compounds 1-PF – 6-PF

6

2

-1

[

Au(PHEN)(η -nb)][PF ] (1-PF ). Yield 50%; mp 208 °C. Selected IR bands (ν/cm ; KBr

6 6

1

pellet): 2952, 2925, 2854, 1509, 1500, 1449, 1381, 1319, 867, 838 ν(PF ), 779, 728. H

6

NMR (CD Cl ): δ 0.81 (d, 1H, J =10.1 Hz; CH H-7), 1.25 (2d, overlapped, 3H, J = 11.9, 8.3

2

syn

Hz; CHH -7 + CHH-5,6), 1.80 (d, 2H, J = 8.3 Hz; CHH-5,6), 3.31 (s, 2H, CH-1,4), 4.40 (s, 2H,

anti

HC=CH), 8.19 (s, 2H; H-3ꞌ), 8.21 (d, 2H, J = 4.9 Hz; H-6ꞌ), 8.80 (d, 2H, J = 8.3 Hz; H-4ꞌ), 9.26

1

(

d, 2H, J = 4.6 Hz; H-2ꞌ). H NMR (CD CN): δ 0.74 (d, 1H, J = 9.7 Hz; CH H-7), 1.19 (2d,

3

syn

overlapped, 3H, J = 13.6, 7.6 Hz, CHH -7 + CHH-5,6), 1.74 (d, 2H, J = 7.6 Hz; CHH-5,6),

anti

3

.25 (s, 2H; CH-1,4), 4.35 (s, 2H; HC=CH), 8.15 (dd, 2H, J = 8.3, 4.8 Hz; H-3ꞌ), 8.17 (s, broad,

1

3

2

H, H-6ꞌ), 8.81 (dd, 2H, J = 8.3, 1.4 Hz; H-4ꞌ), 9.24 (dd, 2H, J = 4.8, 1.4 Hz; H-2ꞌ). C NMR

2

0

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

(

CD CN): δ 25.79 (2C, CH -5,6), 43.51 (2C, CH-1,4 ), 44.23 (1C, CH -7), 84.02 (2C, =CH),

3

2

1

27.57 (2C, CH-3ꞌ), 128.99 (2C, CH-6ꞌ), 131.68 (2C, C5ꞌ), 141.69 (2C, CH4ꞌ), 144.82 (2C, C7ꞌ),

53.57 (2C, CH2ꞌ).

1

2

-1

[

Au(NCP)(

η

-nb)][PF ] (2-PF ). Yield 82%; mp 244 °C. Selected IR bands (ν/cm ; KBr pellet):

6

1

8

38 ν(PF ). H NMR (CD Cl ; assignments based on NOESY and HSQC experiments): δ 0.87

6

2

(

d, 1H, J = 9.9 Hz; CH H-7), 1.29 (2d, overlapped, 3H, J = 8.5 Hz; CHH -7 + CHH-5,6), 1.83

syn anti

(d, 2H, J = 8.1 Hz; CHH-5,6), 3.27 (2s, overlapped, 8H; 2Me + CH-1,4), 4.30 (s, 2H, HC=CH),

1

3

8

.04 (d, 2H, J = 8.0 Hz; H-3ꞌ), 8.07 (s, 2H, H-6ꞌ), 8.64 (d, 2H, J = 8.0 Hz; H-4ꞌ). C NMR

(

CD Cl ): δ 25.83 (2C, CH -5,6), 28.68 (2C, CH ), 43.11 (2C, CH-1,4), 43.71 (1C, CH -7),

2 2 2 3 2

8

2.57 (2C, =CH), 127.17 (2C, CH-6ꞌ), 127.26 (2C, CH-3), 129.05 (2C, C-5ꞌ), 140.90 (2C, CH-

31

1

4

ꞌ), 143.92 (2C, C-7ꞌ), 161.16 (2C, C-2); P{ H} NMR (CD Cl ): δ -144.53 (m, J = 710 Hz,

2 2

PF₆).

2

-1

[

Au(4,7-DMP)(

η -nb)][PF ](3-PF ). Yield 52%; m.p. 209.6 °C. Selected IR bands (ν/cm ; KBr

6 6

1

pellet): 838 ν(PF ). H NMR (CD Cl ): δ 0.68 (d, 1H, J = 11.4 Hz; CH H-7), 1.24 (2d,

6

2

syn

overlapped, 3H, J = 12.2, 6.0 Hz; CHH -7 + CHH-5,6), 1.78 (d, 2H, J = 8.1 Hz; CHH-5,6),

anti

2

.99 (s, 6H, 2CH ), 3.28 (s, 2H; CH-1,4), 4.29 (s, 2H, HC=CH), 7.97 (s broad, 2H, H-3ꞌ), 8.32 (s,

3

1

broad, 2H, H-6ꞌ), 9.07 (s, broad, 2H, H-2ꞌ). H NMR (CD CN): 0.72 (d, 1H, J = 9.7 Hz; CH H-

3

syn

7

), 1.18 (2d, overlapped, 3H, J = 10.6, 3.5 Hz; CHH -7 + CHH-5,6), 1.73 (d, 2H, J = 7.3 Hz;

anti

CHH-5,6), 2.93 (s, 6H; 2Me), 3.23 (s, 2H; CH-1,4), 4.26 (s, 2H, HC=CH), 7.98 (s, broad, 2H; H-

1

3

ꞌ), 8.34 (s, 2H; H-6ꞌ), 9.09 (s broad, 2H; H-2ꞌ). C NMR (CD CN): δ 18.22 (2C, Me), 24.31

3

(

2C, CH -5,6), 41.86 (2C, CH-1,4), 42.49 (1C, CH -7), 81.34 (2C, =CH), 123.41 (2C, CH-3ꞌ),

2

1

26.17 (2C, CH-6ꞌ), 129.17 (2C, C5ꞌ), 143.04 (4C, C4ꞌ+C7ꞌ), 150.89 (2C, CH-2ꞌ).

2

-1

[

Au(TMP)(

η

-nb)][PF ] (4-PF ). Yield 38%; mp 246 °C. Selected IR bands (ν/cm ; KBr

6

1

pellet): 838 ν(PF ). H NMR (CD Cl ): δ 0.79 (d, 1H, J = 9.0 Hz; CH H-7), 1.23 (2d,

6

2

syn

overlapped, 3H, J = 8.6, 6.7 Hz; CHH -7 + CHH-5,6), 1.79 (d, 2H, J = 7.3 Hz; CHH-5,6), 2.86

anti

(

s, 6H; CH ), 2.70 (s, 6H; CH ), 3.29 (s, 2H; CH-1,4), 4.27 (s, 2H; HC=CH), 8.31 (s, broad, 2H,

3 3

1

H-6ꞌ), 8.95 (s, broad, 2H, H-2ꞌ). H NMR (CD CN): δ 0.70 (d, 1H, J = 9.5 Hz; CH H-7), 1.13

3

syn

(

dd, 1H, J = 4.4, 2.4 Hz; CHH -7), 1.17 (dd, 2H, J = 10.1, 2.5 Hz; CHH-5,6), 1.73 (d, 2H, J =

anti

7

.5 Hz; CHH-5,6), 2.60 (s, 6H, Me), 2.67 (s, 6H; Me), 3.22 (s, 2H; CH-1,4), 4.19 (s, 2H;

1

3

HC=CH), 8.22 (s, 2H; H-6ꞌ), 8.91 (s, 2H; H-2ꞌ). C NMR (CD CN): δ 15.64 (2C; Me), 17.88

3

(

2C; Me), 25.77 (2C; CH -5,6), 43.26 (2C; CH-1,4), 43.84 (1C; CH -7), 82.35 (2C; =CH),

2

1

24.67 (2C; CH-6ꞌ), 129.54 (2C; C5ꞌ), 136.02 (2C; CH-3ꞌ), 142.99 (2C; C4ꞌ), 149.34 (2C; C7ꞌ),

53.60 (2C; C2ꞌ).

1

2

1

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

2

-1

[

Au(BTP)(

η

-nb)][PF ] (5-PF ). Yield 29%; mp 165.8 °C. Selected IR bands (ν/cm ; KBr

6

1

pellet): 838 ν(PF ). H NMR (CD Cl ): δ 0.85 (d, 1H, J = 10.1 Hz; CH H-7), 1.28 (m, broad,

6

2

syn

3

2

H; CHH -7 + CHH-5,6), 1.82 (d, 2H, J = 9.0 Hz; CHH-5,6), 3.34 (s, 2H; CH-1,4), 4.40 (s,

anti

H; HC=CH), 7.66 (m, 10H, J = 9.5 Hz; H-o+H-m+H-p Ph), 8.11 (d, 2H, J = 6.0 Hz; H-3ꞌ), 8.18

1

(

s, 2H; H-6ꞌ), 9.28 (d, 2H, J = 5.1 Hz; H-2ꞌ). H NMR (CD CN): δ 0.80 (d, 1H, J = 10.3 Hz;

3

CH H-7), 1.21 (dd, 2H, J = 2.3, 7.7 Hz; CHH-5,6), 1.29 (d, 1H, J = 9.7 Hz; CHH -7), 1.78 (d,

syn

anti

2

H, J = 9.1 Hz; CHH-5,6), 3.31 (s, 2H; CH-1,4), 4.40 (s, 2H; HC=CH), 7.67 (s, 10H, Ph), 8.06

1

3

(

broad d, 2H, CH-3ꞌ), 8.14 (s, 2H, H-6ꞌ), 9.35 (broad d, 2H, J = 4.6 Hz; H-2ꞌ). C NMR

(

CD CN): δ 24.29 (2C; CH -5,6), 41.96 (2C; CH-1,4), 42.66 (1C; CH -7), 82.16 (2C; =CH-2),

3

2

1

25.23 (2C; CH-3ꞌ + CH-5ꞌ), 126.14 (Ph), 128.81 (Ph + C-6ꞌ), 129.41 (Ph), 144.00 (2C; C-7ꞌ),

3

1

51.57 (2C; CH-2ꞌ); P{ H} NMR (CD Cl ): δ -144.53 (m, J = 710 Hz; PF ).

2

6

2

-1

[

Au(BTC)(η -nb)][PF ] (6-PF ). Yield 36%; mp 187 °C. Selected IR bands (ν/cm ; KBr pellet):

6 6

1

8

38 (PF ). H NMR (CD Cl ): δ 0.90 (d, 1H, J = 9.8 Hz; CH H-7), 1.32 (m, broad, 3H;

6 2 2 syn

CHH -7 + CHH-5,6), 1.85 (d, 2H, J = 8.6 Hz; CHH-5,6), 3.30 (s, 2H; CH-1,4), 3.32 (s, 6H;

anti

CH ), 4.31 (s, 2H; HC=CH), 7.63 (m, broad, 10H, H-o+H-m+H-p Ph), 7.97 (s, 2H; H-3ꞌ), 8.04 (s,

3

1

2

H; H-6ꞌ). H NMR (CD CN): δ 0.81 (d, 1 H, J = 9.8 Hz; CH H-7), 1.24 (dd, 2H, J = 7.9, 2.4

3

syn

Hz; CHH-5,6), 1.31 (dd, 1H, J = 9.7 Hz; CHH -7), 1.78 (d, 2H, J = 8.4 Hz; CHH-5,6), 3.25 (s,

anti

2

4

1

H; CH-1,4) 3.26 (s, 6H; Me), 4.31 (s, 2H; HC=CH), 7.62 (m, 10H; H-o+H-m+H-p Ph), 7.98 (s,

1

3

H; H-3ꞌ), 8.03 (s, 2H; H-6ꞌ). C NMR (CD CN): δ 25.79 (4C, overlapping; CH -5,6 + CH ),

3

2

3

3.51 (2C; CH-1,4), 44.20 (1C; CH-7), 84.04 (2C; =CH), 127.57 (4C, overlapping; CH-3ꞌ + C5ꞌ),

28.99 (Ph + CH-6ꞌ), 131.68 (Ph), 141.69 (Ph), 144.81 (4C, overlapping; C-7ꞌ + C-4ꞌ), 153.57

(2C; C-2ꞌ).

Electronic Supplementary Information (ESI) available. Experimental data including

information on X-ray data collection and structure determination, full crystallographic data,

1

13

NMR spectra ( H, C). This material is available free of charge via the Internet at XXXXX.

Crystallographic data of 1-PF (CCDC 1901009), 2-PF (CCDC 1901011) and 6-PF (CCDC

6

1

901010) can be obtained free of charge from the Cambridge Crystallographic Data Center via

www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgements. Regione Autonoma della Sardegna (RAS) is kindly acknowledged for the

financial support coming from L.R. 7, CRP-78365. M. A. acknowledges Dipartimento di Scienze

Chimiche e Geologiche and Fondazione Banco di Sardegna for support (PRID 2015). F. O.

2

European Journal of Inorganic Chemistry

10.1002/ejic.201901116

would also like to acknowledge Dr. Chris Muryn, the X-ray service at the School of Chemistry

UoM) and the Engineering and Physical Sciences Research Council (Grant EP/K039547/1) for

support. AP acknowledges RAS for the funding in the context of the POR FSE 2014 – 2020

CUP F24J17000190009).

(

Notes

The authors declare no competing financial interest.

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Structural, Theoretical and Spectroscopic Characterisation of a Series of Novel Gold(I)-Norbornene Complexes Supported by Phenanthrolines: Effects of the Supporting Ligand

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