Molecular Orbital Analysis of Bonding in ReH92- and [ReH8{PH3

15 Molecular Orbital Analysis of Bonding in ReH9 and [ReH {PH }] 2-

8

-

3

A. P. GINSBERG

Downloaded by CORNELL UNIV on June 12, 2017 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch015

Bell Laboratories, Murray Hill, NJ 07974

Self-consistent field Xα-scattered wave calculations were car ried out for the hydride complex ReH , its monophosphine derivative, equatorial [ReH {PH } , and the ligand array H . The results lead to the following significant conclusions. (1) H-H bonding interactions contribute to the stabilization of the complexes. (2) Replacing an equatorial hydrogen of ReH with PH causes the net atomic charges to change from —0.19 to +0.17 for Re, from —0.24 to —0.11 for apical hydrogen, and from —0.12 to —0.09 for equatorial hydrogen. The PH group takes on a net negative change (—0.31). (3) Re 5d —> Ρ 3d π backbonding is a minor effect compared with Ρ 3p—>Re 5d σ donation. The net transfer of negative charge in PH largely results from R e - Η —> Ρ σ donor interactions. 92-

8

3

-

92-

92-

3

3

3

C

ompounds

containing

hydrogen

a n d tertiary

phosphine

ligands

bound to a rhenium atom comprise a large class of hydride complexes ( J , 2).

These m a y be regarded as derivatives of the enneahydriderhenate ion, R e H ~ , 9

m a n y of w h i c h m a y be synthesized b y reaction of R e H tertiary phosphine (3, 4).

9

2

2

~ w i t h the appropriate

E l e c t r o n i c structure a n d b o n d i n g i n these h y d r i d e

complexes is not well understood; i n particular, the following interesting questions have not been answered. (1) W h a t is the contribution of H - H interaction to the b o n d i n g i n the p o l y h y d r i d o complexes? (2) W h a t is the effect on the charge distribution of r e p l a c i n g a h y d r i d e l i gand b y a tertiary phosphine group? (3) Does the phosphine group function s i m p l y as a σ donor, or is there a significant amount of R e 5d —+ Ρ 3 d π b a c k b o n d i n g ? T o investigate these questions, I carried out self-consistent field Xa-scattered wave ( S C F - X a - S W ) calculations (5, 6) on R e H ~ , its monophosphine derivative, equatorial [ R e H i P H } ] ~ , and the l i g a n d array H " . ( [ R e H g j P H s ) ] serves as a m o d e l for the k n o w n anions [ R e H L ] " L = ( C H ) P , ( C H ) 3 P , a n d ( n 9

8

3

2

9

8

2

-

6

5

3

2

5

0-8412-0390-3/78/33-167-201/$05.00/0 © American Chemical Society Bau; Transition Metal Hydrides Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

202

TRANSITION M E T A L HYDRIDES

C^g^P.

In terms of the shift i n C O stretching frequencies i n phosphine metal

c a r b o n y l complexes, PH3 is less basic (or more π-acid) than t r i a l k y l or t r i a r y l phosphines (7, 8, 9).)

T h e results, reported i n this chapter, lead to the following

significant conclusions. ( 1 ) H - H b o n d i n g interactions contribute to the stabilization of the c o m plexes. (2) R e p l a c i n g an equatorial hydrogen of R e H

9

2

~ w i t h P H causes the net 3

atomic charges to change f r o m —0.19 to +0.17 for Re, f r o m —0.24 to —0.11 for apical hydrogen, and f r o m —0.12 to —0.09 for equatorial hydrogen.

The P H

3

group takes on a net negative charge (—0.31). (3) Re 5d —• Ρ 3d π b a c k b o n d i n g is a m i n o r effect c o m p a r e d w i t h Ρ 3p —• Re 5d σ donation. T h e net transfer of negative charge to P H largely results from Downloaded by CORNELL UNIV on June 12, 2017 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch015

3

R e - H —• Ρ σ donor interactions. Procedure for

Calculations

S C F - X a - S W calculations were executed i n double precision on a H o n e y w e l l 6000 computer using current versions of the programs w r i t t e n o r i g i n a l l y by K . H . Johnson a n d F . C . Smith. F i g u r e 1 shows the coordinate axes and the geometry of the systems studied. R e H g was assumed to have D / , s y m m e t r y , as f o u n d b y neutron d i f f r a c t i o n on K^ReHg (10). T h e average measured R e - Η distance (1.68 A) and the H - R e - H angle shown i n F i g u r e 1 were used to determine hydrogen coordinates i n atomic units (1 bohr = 0.52917 Λ). T h e H calculation u t i l i z e d the same s y m m e t r y and coordinates as those for R e H g . T h e calculation for [ R e H s i P H ! ] ~ was carried out for the equatorial isomer w i t h C symmetry. (The nine-coordinated 2 -

3

9

2

_

2 -

3

s

Figure 1. (a) ReH ~ 2

9

Coordinate system, geometry, and hydrogen kbeling scheme, and tf ~ ( D ) ; (b) \ReH \PH^\\- ( C ; σ in the xz plane). 2

9

3 h

H

s

η

Bau; Transition Metal Hydrides Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

15.

Bonding in ReH ~

GINSBERG

T a b l e I.

2

9

System


H

9

2

203

[ReH \PH \]~ H

3

E x c h a n g e Parameters a n d Sphere R a d i i (Atomic Units) for R e H , H " and [ R e H | P H } ] 9

ReH9

and

2

"

[ReH (PH |]8

3

2

9

2

8

3

a

Region

a

R

Re H Re OUT INT

0.69325 0.77725 0.77725 0.72879

2.481 1.488 4.365

H OUT INT

0.77725 0.77725 0.77725

2.352 5.057

Re HRe Ρ

0.69325 0.77725 0.72620 0.77725 0.77725 0.72990

2.481 1.488 2.220 1.407 6.272

HP

OUT INT

—

—

—

O U T refers to the outer sphere surrounding the entire cluster, and I N T refers to the regions between the atomic spheres and inside the outer sphere. H R represents hydrogen bound to rhenium, and H p represents hydrogen bound to phosphorus. a

c

[ReH |PR3l] anions presumably retain the R e H 9 structure with the phosphine substituted i n an equatorial or an a p i c a l position. L o w temperature ir studies (4) on [ R e H ( P P h | ] suggest that it m a y be a m i x t u r e of both isomers. X - r a y diffraction studies on R e H y j P N / P h t a (11) show the phosphorus atoms i n positions consistent w i t h equatorial substitution i n the R e H 9 structure.) R h e n i u m a n d r h e n i u m - b o n d e d hydrogen coordinates were the same as those for R e H 9 2 ; the phosphorus atom was located on the x-axis 2.34Å f r o m the r h e n i u m . (In H R e 2 ( P E t 2 P h ) , w i t h essentially the same t e r m i n a l R e - Η distance as R e H 9 , the R e - P distance is 2.335Å (12). A similar R e - P distance has been found i n ReH (diphos)2 (IS).) T h e phosphorus-bonded h y d r o g e n coordinates were derived f r o m the k n o w n structure of P H ( P - H = 1.415 α a n d angle H - P - H = 93.45°) (14,15). 2

8

8

3

2

_

8

2

4

3

3

T a b l e I summarizes the α-exchange parameters and sphere r a d i i used i n the calculations. T h e α value for hydrogen is that recommended by Slater (16); the same value was used for the extramolecular region. F o r phosphorus, a n F was taken f r o m S c h w a r z s table (17) w h i l e the α value for r h e n i u m was deter m i n e d by c o m p u t i n g α τ as described by Schwarz (17). In the intersphere re gions, a weighted average α was used where the weights were the n u m b e r o f valence electrons i n the atoms. O v e r l a p p i n g atomic sphere r a d i i for R e H 9 were d e t e r m i n e d by N o r m a n s Procedure (18). T h e same r a d i i were used for [ R e H j P H } ] together w i t h the Ρ a n d H sphere r a d i i used for the free P H molecule (19). O v e r l a p p i n g atomic sphere r a d i i for the H 9 system were obν

2

8

3

P

3

2


204


tained by increasing the radii of touching atomic number spheres (18) by 25% (20) without attempting optimization with respect to the virial ratio. In each case, the outer sphere was taken to be tangent to the outermost touching atomic number spheres, which gave an overlapping outer sphere for the actual atomic sphere radii (18). The outer sphere was centered at the origin for R e H ~ and H ~ , for [ReH |PH3J]~ it was centered at the valence electron-weighted average of the atom positions. A Watson sphere (21 ), concentric with the outer sphere 9

9

2

2

8

T a b l e II. G r o u n d - S t a t e V a l e n c e L e v e l E i g e n v a l u e s , Ionization Energies, a n d C h a r g e Distributions for H g and R e H ~ 2 -

9

2

»~


H

Eigenvalue (Ry) -0.172 -0.302 -0.302 -0.452 -0.574 -0.807

Level 2αΊ le" 2e' le' la" la'i c

2

2

Charge Distribution (%) OUT H7-9 14 53 10 0 5 45 6 38 7 0 4 29

a

Hl-6 23 84 34 46 91 66

INT 9 6 16 9 2 0

ReH ~ 2

9

Level

Eigen value (Ry)

I.E. (eV)

Charge Distribution (%) Re Hl-6 H7-9 OUT INT

lla'i 9e' 6a "2 ΙΟαΊ 8e' 4e" 9a'i le' 5a "2 8a i

-0.005 -0.556 -0.573 -0.619 -0.625 -0.700 -0.839 -3.143 -3.149 -5.008

10.6 10.8 11.6 11.6 12.8 14.5 46.7 46.8 72.3

2 28 11 52 20 49 18 98 98 99

c

r

a

0 37 53 12 3 42 34 1 2 0

2 5 0 23 35 0 19 0 0 0

95 11 17 5 2 5 11 0 0 0

1 19 19 8 40 4 17 0 0 0

Major Re Spher. Harmonic b

d 2—y2 y

Px,y>

X

X

Pz d2 z

dx —y ,xy 2

2

dxz,yz

s Px.y

Pz S

Percentage of the total population of the given level located within the indicated regions. H l - 6 refers to the combined prism corner (apical) hydrogen spheres {see Figure 1); Η 7 - Η 9 refers to the combined equatorial hydrogen spheres {see Figure 1); O U T and I N T refer, respectively, to the extramolecular and intersphere regions. T h e major spherical harmonic basis functions in the Re sphere. Highest occupied orbital. a

b

c

and bearing a charge equal in magnitude but opposite in sign to the cluster charge, was used to simulate the electrostatic interaction of the cluster with its surrounding crystal lattice. The highest-order spherical harmonics used to expand the valence level wave functions were 1 = 3 in the extramolecular region, 1 = 2 in the Re and Ρ spheres, and 1 = 0 in the Η spheres. All ground-state S C F calculations converged to better than ±0.0004 Ry for each variance level. Core levels were relaxed in the R e H ~ 9


2


L

y

9

2

\

ν \

\ \

2e',le"

9

H 2-

\ \ \

V .

\

e

H

9

2-

1

9 a

l'

4e"

\ ~~8e

^--^

\\\ \r\~?6a2 finο \\>\10a',

R

29a

-~ "

36 a'

17a"

1

N

13a'

37a'

9

2

["^{ΡΗ^Γ H 8 a " , 38a' 6a,

PH

9

2

3

Figure 2. SCF ground-state one-electron valence energy levels for H ~ , R E H ~ , [ReHs\PH^}]~ and P H 3 . The level at the extreme left marh the degeneracy-weighted center of the H ~ levels. The arrows point to the highest occupied levels. The P H eigenvalues are from Ref 19.

-I0

8H0.222-


206


calculation and were converged to ±0.0026 R y or better. A l l core levels (Re l - 4 s , 2 - 4 p , 3 d , 4 d , a n d 4/; Ρ Is, 2s, a n d 2p) were frozen i n the [ R e H j P H } ] - c a l c u lation. T h e converged ground-state potentials were used to search for excited state levels u p to a m a x i m u m energy of —0.002 R y . F o r R e H , the Slater transition state procedure (5, 6) was used to calculate the ionization energies of the valence levels. 8

3

9

2 _

Results T h e calculated ground-state one-electron valence energy levels and charge distributions for H

9

2

~ , R e H ~ , a n d [ R e H g l P r ^ } ] " are s u m m a r i z e d i n Tables II 9

2

and III. Calculated valence-level ionization energies for R e H ~ are also given Downloaded by CORNELL UNIV on June 12, 2017 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch015

9

2

i n T a b l e II. E x p e r i m e n t a l ionization energies for comparison are not available presently.

F i g u r e 2, a d i a g r a m of the eigenvalues i n Tables II and III, shows the

T a b l e III.

G r o u n d State V a l e n c e L e v e l Eigenvalues

Level

Eigenvalue (Ry)

Re

18a " 38a ' 37a' 17a" 36a'

-0.0055 -0.007 -0.009 -0.014 -0.085

2 2 9 14 19

2 1 4 4 8

0 1 0 0 0

35a'

-0.512

19

6

-0.518 -0.547 -0.581 -0.627 -0.634 -0.681 -0.700 -0.802 -0.806 -0.812 -1.280 -3.098 -3.101 -3.103 -4.952

13 12 49 39 46 44 47 19 2 4 1 98 98 98 99

2 1 10 26 1 4 0 6 39 37 62 0 0 0 0

16a" 34a' 33a' 32a' 15a" 31a' 14a" 30a' 13a" 29a' 28a ' 27a' 12a" 26a' 25a'

c

Charge Distribution Ρ

(% ) —— H4 H2 + H3

H5 +

0 0 1 2 1

0 1 0 0 0

0 0 2 0 1

14

6

15

6

0 10 2 1 0 12 0 5 0 1 0 0 0 0 0

20 15 4 0 2 7 20 14 1 1 0 0 0 1 0

0 11 1 1 0 12 0 6 0 0 0 0 0 0 0

19 16 3 0 2 7 23 13 0 3 0 0 0 1 0

HI

a

Percentage of the total population of the given level located within the indicated regions. T h e hydrogen sphere numbers refer to Figure 1. O U T and I N T refer, respectively, to the extramolecular and intersphere regions. a


15.

GINSBERG

Bonding in ReH ~ 2

9

and

207

[ReH \PH \]s

3

correlation between levels in the different systems. Wave function contour maps of selected orbitals are shown in Figures 3, 4,5, and 6. Each map was generated from numerical values of the wave function at 6561 grid points within a 10 X 10 ( H 9 - and R e H 0 ) or 16 X 16 ([ReH {PH ]-) bohr area. 2

2

8

2

3

The ground-state total energies and total charge distributions are given in Table IV.

If the total charge in the intersphere and extramolecular regions is

partitioned among the atomic spheres in proportion to the charge density at the sphere surface, the charge distributions in Table IV lead to the net atomic charges listed in Table V. In the case of T c H

2

9

, net atomic charges derived by this

method from the SCF-Xa-SW total charge distribution (4) can be compared with the net charges given by an S C F Gaussian orbital calculation (22).


in Table V , the agreement is excellent.

As shown

(Partitioning the intersphere and ex

tramolecular charge among the atoms proportionally to the number of valence electrons within each atomic sphere (23) leads to results similar to those in Table

and C h a r g e Distributions for [ R e H l P H J ] 8

Charge Distribution + H8 1 0 0 0 1

H9 0 0 1 0 0

H10 + H11 0 0 0 1 1

3

(% )

IrmoIc

OUT

INT

82 80 72 42 40

13 14 11 35 29

Ρ

Re

dy

Z

d 2- 2, x

y

d2 z

3

1

1

3

26

Px

Px, d 2- 2 x

11 0 16 14 35 0 0 11 0 0 0 0 1 0 0

0 1 1 2 0 5 0 2 0 28 10 0 0 0 0

1 1 1 4 2 2 0 1 48 15 20 0 0 0 0

2 2 1 2 1 1 0 1 3 3 2 0 0 0 0

30 30 12 12 10 5 8 23 7 8 3 0 0 0 0

y

Py Pz

dxy d Px Px dxy d , Ρζ xz

d2 z

d 2- 2 x

y

d dy s

xz

xz

Z

Px Py, d Pz, d s

xy

d

xz

xz

Px Py Pz s

T h e major Re and Ρ spherical harmonic basis functions. Highest occupied orbital.



208


Figure 3. Wavefunction contour maps of the H 9 molecular orbitals. Solid and broken lines denote contours of opposite sign having magnitudes indicated by the numerical labels: 1,2,3,4 = 0.02,0.04,0.06,0.08, respectively. Maps in the HI, H2, and H3 plane show apical-apical interactions; maps in the H2, H3, and H8 plane show equatorial-apical interactions. A marks the position of H atom centers. 2

Table IV. G r o u n d - S t a t e T o t a l Energies (Rydbergs) a n d T o t a l C h a r g e Distributions for H ReH and [ R e H ( P H | ] 9

2

H 29

T o t a l energy -8.4739 K i n e t i c energy, Τ 9.3033 -17.7772 Potential energy, V 1.047 -2T/V Intersphere potential -0.0948 energy T o t a l charge (electrons) i n various regions — Re apical Η 6.01 equatorial Η 3.47 — Ρ — phosphine Η extramolecular 0.63 intersphere 0.89

9

2

8

ReH 2

9

-31579.3048 31579.6832 -63158.9880 1.000006 -0.6072

73.39 5.34 2.45 — — 1.38 3.43

3

[ReH \PH \]8

3

-32274.4659 32258.3258 -64532.7917 0.999750 -0.4064

73.79 5.59° 1.81 13.89 2.95 0.45 3.51 fc

T h e nonequivalent apical hydrogen spheres have similar total charges: H I , 0.92; H 2 + H3,1.85; H 4 , 0.92; H 5 + H 6 , 1.86. Each of the phosphine hydrogen spheres has the same total charge. a

6


15.

GINSBERG

Table V .

Bonding in ReHg ~ and [ReH%\PHz\]~

209

2

Net A t o m i c Charges i n H 9 2 - , R e H 9 2 , [ R e H ( P H ) ] - , a n d TcH92_

8

SCF-GO TcH

3

a

Atom

ReH

2

9

Re or T c Apical H Equatorial H Ρ Phosphine Η

-0.16 -0.34 — —

-0.19 -0.24 -0.12 — —

[ReH \PH ]] |s

3

+0.17 -0.11 -0.09 +0.32 -0.21

2

9

SCF-Xa TcHf-

-0.37 -0.20 -0.14 — —

c c

b

-0.33 -0.22 -0.12 — —

From a Hartree-Fock-Roothan S C F calculation in a contracted Gaussian orbital basis (22). From an S C F - X o r - S W calculation; intersphere and extramolecular charge partitioned by the same method described for R e H o (4). T h e S C F - X a - S W total charge distribution for the free P H molecule ( 19) leads to the following net atomic charges if the intersphere and extramolecular charge are partitioned as described in the text: Ρ, +0.51 and H , - 0 . 1 7 . a

b

2 -


c

3

Figure 4. Wave function contour maps for ReH molecular orbitals. Contour values and sign convention as in Figure 1. Interior contours close to the rhenium atom center have been omitted. Η atom centers are marked by*. 2


210



32a' (Re, R H7, H8)

29a' (Re, P, HI, H4, H9)

13a" (Re, Ρ, H7, H8)

31a' (Re, P, HI, H4, H9)

15a" (Re, P, H7, H8)

34a' (Re, P, HI, H4, H9)

16a" (Re,P, H7, H8)

Figure 5. Wave)unction contour maps for the major Re-P σ bonding orbital (32a') of [ReHs\PH^\]~ and the orbitals in which Re-P π bonding is allowed by symmetry. Contour values and sign convention as in Figure 1. Interior contours close to the Re and Ρ atom centers have been omitted. Η atom centers are marked by : V.

However, the partitioning method used to derive T a b l e V is preferred since,

for the

C3O2

molecule (24), it leads to results i n closer agreement w i t h X P S

measurements and ab initio calculations.) Discussion T o separate H - H f r o m R e - Η interactions, it is appropriate to e x a m i n e the interactions i n the H g ligand array and to compare the molecular orbitals (MOs) for this system w i t h those of R e H g . T h e choice of the —2 charge on the ligand array to be studied is consistent w i t h the small value for the calculated net charge on Re (Table V ) . 2 -

2 -

F r o m the large M O splittings found for H ~ (see T a b l e II and F i g u r e 2), it is evident that strong interactions exist between the hydrogen Is orbitals i n this system. T h e interactions contributing to each of the M O s m a y be inferred from the charge distributions i n T a b l e II and the contour diagrams i n F i g u r e 3. T h e major interactions take place between a p i c a l atoms w i t h i n the triangular p r i s m faces ( a p i c a l - a p i c a l interaction; d(H-H) = 1.99 A) a n d between an equatorial atom and the apical atoms i n the nearby square p r i s m face ( e q u a t o r i a l - a p i c a l interaction; d ( H - H ) = 1.93 A). I n the lowest l y i n g M O , Ι α Ί , only b o n d i n g i n 9

2


15.

Bonding in ReH ~ and

GINSBERG

2

9

211

[ReH \PH^]~ s

teractions, both a p i c a l - a p i c a l a n d e q u a t o r i a l - a p i c a l occur.

In the l a " 2 orbital,

the charge on the equatorial atoms is zero and only b o n d i n g a p i c a l - a p i c a l i n teractions take place. to levels \e and 2e'.

Both b o n d i n g and a n t i b o n d i n g interactions contribute In both of these orbitals and a p i c a l - a p i c a l interactions are

f

p r e d o m i n a n t l y antibonding, but the e q u a t o r i a l - a p i c a l interactions are pre d o m i n a n t l y b o n d i n g i n \e' and a n t i b o n d i n g i n 2e'.

T h e le"

orbital, w i t h zero

charge on the equatorial atoms, has only a p i c a l - a p i c a l interactions and these are predominantly antibonding.

T h e highest l y i n g orbital of the H g ~ system, 2 α Ί , 2

is d o m i n a t e d by antibonding e q u a t o r i a l - a p i c a l interactions. T h e correlation between H g

2 -

and R e H g

2 -

M O s (Figure 2) and comparison

of the charge distribution and contour maps for corresponding orbitals (Table II and F i g u r e 4) lead to the conclusion that H g ~ H - H b o n d i n g orbitals preDownloaded by CORNELL UNIV on June 12, 2017 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch015

2

30α' (Re,P,H7,H8)

' V '

30 d' (Ρ, H2.H3)

/ Re

\

^

'Λ Χ

\

" 33Q (Re,P,H7, H8)

o

"

35Q (P,H2,H3)

Figures 6. Wave function contour maps for or bitals in which Re-H—Ρ bonding interactions occur. Contour values and sign convention is in Figure 1. Interior contours close to the Re and Ρ atom centers have been omitted. Η atom centers are marked by ·


212


d o m i n a t e over H - H a n t i b o n d i n g orbitals i n c o n t r i b u t i n g to the R e H g M O s . It follows from this that a net H - H bonding interaction exists i n the R e H g anion. In support of this conclusion, the two strongly H - H bonding orbitals of H g (la\ and la"2) correlate w i t h predominantly hydrogen-based orbitals i n R e H g . It is evident from Figures 2, 3, and 4 that the la"2 ( H g ) orbital is perturbed only slightly by formation of the 6a" ( R e H g ) orbital; the contour maps suggest a slight enhancement of the H - H interaction. A more substantial perturbation occurs when the la'γ ( H g ) orbital interacts w i t h a Re 6s orbital to f o r m the 9a'\ ( R e H g ) M O ; again the contour maps indicate enhanced H - H b o n d i n g i n the complex (Figure 4). B y contrast, the two most strongly H - H antibonding levels of H g (le" and 2aΊ) correlate w i t h predominantly metal-based levels i n R e H g and are perturbed strongly by the interaction w i t h r h e n i u m . C o m p a r i s o n of the appropriate parts of Figures 3 and 4 shows how the 2a'\ ( H g ) orbital is altered by interaction w i t h a Re 5d 2 orbital to f o r m the ΙΟαΊ ( R e H g ) M O . T h e latter retains the e q u a t o r i a l - a p i c a l H - H a n t i b o n d i n g interaction of its parent but has enhanced a p i c a l - a p i c a l a n d e q u a t o r i a l - e q u a t o r i a l H - H b o n d i n g interactions. O r b i t a l 4e" ( R e H g ) retains, like its parent le" ( H g ) , a p i c a l - a p i c a l H - H a n tibonding. T h e a p i c a l - a p i c a l antibonding interaction found i n orbitals le' and 2e' of H is present i n 9e' ( R e H g ) but not 8e' ( R e H g ) . Neither of the latter two orbitals show the e q u a t o r i a l - a p i c a l interactions of le' a n d 2e' ( H g ) . 2 -

2 -

2 -

2 -

2 -

2 -

2

2 -

2 -

2 -

2 -


2 -

2 -

z

2 -

9

2

2 -

-

2 -

2-

2 -

T h e effect on the charge distribution of r e p l a c i n g an equatorial h y d r o g e n ligand w i t h P H is elucidated by T a b l e V . O n e unit of net negative charge is lost i n this replacement: 0 . 1 2 e is associated w i t h the h y d r o g e n that is replaced a n d 0 . 8 8 e comes f r o m the r e m a i n i n g R e H s group. Since PH3 i n the complex has a net charge of —0.31 ( - 0 . 2 1 X 3 + 0.32), there must also be a net transfer of 0.31e" f r o m the R e H s part of the molecule to PH3. R e p l a c i n g an equatorial hydrogen of R e H g w i t h P H 3 therefore results i n a loss of 1 . 1 9 e f r o m the re m a i n i n g R e H s group. About 66% of the charge removed f r o m the R e H s group comes f r o m the apical hydrogen atoms, 30% is f r o m the Re atom, and 4% is f r o m the two equatorial hydrogen atoms. T h e hydrogen atoms r e m a i n negatively charged, w i t h the a p i c a l and equatorial charge nearly the same, w h i l e the R e atom charge changes f r o m small negative (—0.19) to small positive (+0.17). 3

-

-

2 -

-

T h e decreased m a g n i t u d e of the calculated net hydrogen-atom charges i n [ R e H | P H î ] c o m p a r e d w i t h R e H g is consistent w i t h the smaller value of r ( R e - H ) observed for phosphine octahydride complexes w i t h the less basic phosphines. F o r example, r ( R e - H ) for R e H g is 18.5 c o m p a r e d w i t h 17.3 for [ R e H s J P P h s ! ] - (3). In both R e H g a n d [ R e H t P H ) ] - the m a g n i t u d e of the calculated negative charge on the metal-bonded hydrogen is small. This agrees with an analysis of experimental measurements on a variety of hydride complexes w h i c h concluded that " t h e f o r m a l l y anionic h y d r i d e l i g a n d is very strongly electron donating, b e i n g only slightly negative i n its complexes'* (25). The calculated phosphorus atom charge i n [ReHs(PH3j]" agrees w i t h the experimental indication that phosphorus i n m a n y tertiary phosphine complexes has a charge of + 0.3 (25). H o w e v e r , the conclusion that P H i n [ R e H s ( P H | ] functions as 3

3

-

2 -

2 -

2 -

8

3

3

3

-


213

2

15. GINSBERG

Bonding in ReH ~ and [ReH \PH \]9

s

3

an electron-withdrawing group diverges from what is found for a tertiary alkyl or phenyl phosphine in complexes such as MCl (PR ) , where the phosphine group serves as a good electron donor (25). Also, recent SCF-Χα calculations on Pt(PH ) L (23) lead to estimated net charges on Ρ of +0.36 (L = 0 ) and +0.33 (L = C2H4) and corresponding net charges for P H of +0.09 and +0.06. The net electron-withdrawing behavior of P H in [ReH (PH }]~ results mainly from charge transfer to the phosphine via Ρ—Η-Re interactions (see below). The Re-P bond in [ReH8JPH |]~ can be appraised by examining the charge distributions (see Table III) and contour maps (Figure 5) for the orbitals that contribute to this bond. By far the major contribution comes from the σ Re(5d 2_ 2)-P(3p ) interaction in orbital 32α'. Comparison of the charge dis tribution in this orbital with the charge distribution in the parent lone-pair 5a 1 orbital of the free P H molecule shows about a 30% loss of charge from P H re sulting from σ-donation. (The charge distribution in the 5a 1 orbital of PH , calculated with the same sphere radii used for [ReHg—»(PH }]~, is: %P, 50; %3H, 12; %OUT, 16; and %INT, 22.) The charge lost by σ-donation is compensated for by transfer of charge on to the P H molecule via interaction of the P(3p ) orbital with the apical and equatorial hydrogen atoms in MOs 30α', 33α', and 35a'. Contour maps showing the Ρ—Η-Re interactions are exhibited in Figure 6. Charge transfer to P H via π back donation from rhenium to phosphorus 3d orbitals is small. This is clear from the contour maps in Figure 5 that show all of the orbitals in which a Re-P π interaction is allowed by symmetry. Two of the orbitals in Figure 5, 29a ' and 13a", show what can be described as a P-H —• Re donor π interaction. Orbitals 31α', 34a , 15a", and 16a" encompass the Re —• Ρ π back donation and evidently do not make an important contribution to the Re-P bond. The negative charge on P H in [ReHsJPH J]~ is a consequence of Re-H —• Ρ σ donor interactions, not of Re —* Ρ π back donation. n

3

3

n

2

2

3

3

8

3

3


x

?/

x

3

3

3

3

3

x

3

7

3

3

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Kaesz, H. D., Saillant, R. B., Chem. Rev. (1972) 72, 231. Giusto, D., Inorg. Chim. Acta, Rev. (1972) 6, 91. Ginsberg, A. P., Chem. Commun. (1968) 857. Ginsberg, A. P., unpublished data. Johnson, Κ. H., Annu. Rev. Phys. Chem. (1975) 26, 39. Slater, J. C., "The Self-Consistent Field of Molecules and Solids: Quantum Theory of Molecules and Solids, Volume 4," McGraw-Hill, New York, 1974. Fischer, E. O., Louis, E., Schneider, R. J. J., Angew. Chem. Int. Ed. Engl. (1968) 7, 136. Klanberg, F., Muetterties, E. L., J. Am. Chem. Soc. (1968) 90, 3296. Tolman, C. Α., J. Am. Chem. Soc. (1970) 92, 2953. Abrahams, S. C., Ginsberg, A. P., Knox, K., Inorg. Chem. (1964) 3, 558. Bau, R., Carroll, W. E., Hart, D. W., Teller, R. G., Koetzle, T. F., ADV. CHEM. SER. (1978) 167, 73. Bau, R., Carroll, W. E., Teller, R. G., Koetzle, T. F., J. Am. Chem. Soc. (1977) 99, 3872 Albany V. G., Bellon, P. L., J. Organomet. Chem. (1972) 37, 151. Kuchitsu, K., J. Mol. Spectrosc. (1961) 7, 399.


214 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

TRANSITION METAL HYDRIDES

Sirvetz, M. H., Weston, R. E., J. Chem. Phys. (1953) 21, 898. Slater, J. C., Int. J. Quantum. Chem. (1973) 7s, 533. Schwarz, K., Phys. Rev. B:5 (1972) 2466. Norman, J. G., Jr., Mol. Phys. (1976) 31, 1191. Norman, J. G., Jr., J. Chem. Phys. (1974) 61, 4630. Salahub, D. R., Messmer, R. P., Johnson, K. H., Mol. Phys. (1976) 31, 529. Watson, R. E., Phys. Rev. (1958) 111, 1108. Basch, H., Ginsberg, A. P., J. Phys. Chem. (1969) 73, 854. Norman, J. G., Jr., Inorg. Chem. (1977) 16, 1328. Ginsberg, A. P., Brundle, C. R., unpublished data. Chatt, J., Elson, C. M., Hooper, Ν. E., Leigh, G. J., J. Chem. Soc. (1975) 2392.


RECEIVED August 16, 1977.


Molecular Orbital Analysis of Bonding in ReH92- and [ReH8{PH3

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