Gas Phase Formation, Structure and Reactivity of Gold Cluster Ions - Gold Clusters, Colloids and Nanoparticles - page 193

Fig. 29 B3LYP/LanL2D6-
31G(d)-calculated potential
energy diagram for the
competing fragmentation
reactions of the model
system (H 3 PAu) 2 H + .
Figure reproduced from
[ 295 ]

phase via CID of the deprotonated amino acid N , N -dimethylglycine (DMG) cluster
ions (R 3 PAu)(R 0 3 PAu)(DMG-H) + , which are formed via electrospray ionisation of
a mixture of the two gold phosphine chlorides, R 3 PAuCl (R Ph and Me), silver

nitrate and the amino acid N , N -dimethylglycine (DMG). For the homodimeric
precursor ions, four fragment channels are observed and include formation of the
ligated dinuclear gold hydride (Eq. ( 35 )); formation of the bis-ligated gold cation,
(R 3 P) 2 Au + (Eq. ( 36 )); loss of the neutral ligated monogold hydride (Eq. ( 37 ));
and formation of the monoligated gold cation, (R 3 P)Au +

¼

(Eq. ( 38 )). In all cases

formation of 2 is the dominant reaction:

þ ½ ð Me 2 NCH 2 CO 2 Þ þ 2AuPR 3

Þ 2 H þ þ ! ð R 3 PAu ½ H 7 ; C 4 ; N ; O 2 ð 35 Þ

Þ 2 Au þ þ ! ð R 3 P Me 2 NCH 2 CO 2 Au ð 36 Þ

þ þ R 3 PAuH

! Me 2 NCH 2 CO 2 ½ ð Þ þ AuPR 3 H ð 37 Þ

R 3 PAu þ þ

! Me 2 NCH 2 CO 2 AuPR 3 ð 38 Þ

Unlike the bare silver hydride, Ag 2 H + , which reacts with a range of substrates
[ 300 , 302 ], 2 is unreactive towards a range of neutral reagents including H 2 O,
MeOH, 2-propanol, acetonitrile, pyridine, allyl iodide, O 2 ,N 2 O, nitromethane and
DMSO. Low-energy CID of 2 proceeds via loss of AuH (Eq. ( 39 )), rather than loss
of R 3 P (Eq. ( 40 )) or direct cluster fragmentation (Eq. ( 41 )). The observed reactivity
is accounted for by the DFT-calculated potential energy diagram of the model
system (H 3 PAu) 2 H + shown in Fig. 29 . Thus both the barrier for isomerisation of 2 to
3 (140.8 kJ mol 1 ) and the final reaction endothermicity for loss of AuH
(126.1 kJ mol 1 ) are lower than the energy required for loss of H 3 P (Eq. ( 40 ),
194.9 kJ mol 1 ) or formation of (R 3 P)Au + (Eq. ( 41 ), 244.8 kJ mol 1 ):

Þ 2 H þ ! R 3 P Þ 2 Au þ þ AuH ð R 3 PAu ð ð 39 Þ

Þ Au 2 H þ þ R 3 P ! R 3 P ð ð 40 Þ

Au þ þ

! ð R 3 P Þ ð R 3 P Þ AuH ð 41 Þ