Would optim work for you?
With this I think you would need to specify an initial parameter guess and a function that returns the negative (log) likelihood. Something like:
# Initial parameter guess
x0 <- 0.0
neg_log_like <- function(x) {
...
}
results <- optim(x0, neg_log_like, method = "Nelder-Mead")
# Print parameter estimate
print(results$par)